The Breathing and Feeding Mechanism of the Lampreys. Ii

When Lampetra wilderi is swimming, the sides of the oral funnel are approximated so that the opening into it is reduced to a narrow vertical slit, fringed by the oral cirri. The compressed oral funnel then serves as a vertical wedge-shaped cut-water. 2. When Lampetra wilderi is about to attach itself to any surface, the oral funnel is spread and applied to the surface with a quick backward and forward movement of the tongue and the animal becomes attached. 3. If an opening is made between the pharyngeal cavity and the exterior in Lampetra wilderi, the animal is still able to attach itself in the same manner as though uninjured. 4. If a communication be established between the mouth cavity or cavity of the oral funnel and the pharyngeal cavity or the exterior, the animal is unable to attach itself. 5. Attachment in Lampetra wilderi is therefore effected by means of a partial vacuum created in the cavities of the oral funnel and mouth by piston-like action of the tongue. 6. A dead Lampetra wilderi becomes firmly attached when its oral funnel is pressed against a surface with the fingers, and remains thus attached. 7. It follows from six that an attached Lampetra wilderi does not necessarily exert muscular energy to maintain its hold. 8. The oral funnel of a dead or living Lampetra wilderi may be moved about freely and very easily over the surface to which it is attached so that the animal is enabled to glide over the surface of its host and so change its position with ease. 9. The oral funnel of a dead or living Lampetra wilderi may be pulled at right angles from the surface to which it is attached only by the exertion of considerable force. 10. It follows from 9 that Lampetra wilderi attached in a current of water may retain its hold without necessarily exerting muscular energy. 11. In inspiration in the attached Lampetra wilderi, water enters each external branchiopore and the nasal tube, coming gently from all directions, just as it enters the mouth of an empty, submerged bottle. It does not enter merely at an angle of 90° to the long axis of the body as stated by Gage for Petromyzon unicolor. 12. In expiration water leaves each external branchiopore in a backwardly directed stream which forms an angle of 45° with the long axis of the body. At the same time a stream issues from the nasal sac. 13. No muscular mechanism has been found to account for the expansion of the gill sacs by means of which inspiration is effected and the inpiration is therefore attributable to the elasticity of the cartilaginous branchial basket. 14. During expiration the gill sacs are compressed and their long axis shortened by the action of the following muscles: a, the internal and external compressors of the gill sac; b, the superficial compressors of the gill pouch (a muscular pouch which encloses each gill sac and is separated from it only by a large lymph space). 15. Water is forced out of the nasal opening at each expiration by the compression of the nasal cœcum between the notochord and the adjacent first and second gill pouches. 16. Water is drawn into the nasal opening at each inspiration by the expansion of the nasal cœcum due to its attachment to the adjacent medial walls of the second and third gill pouches which are separated by the elongation of the axis of these pouches during inspiration. 17. During both inspiration and expiration the external branchiopore has approximately circular form and the valves guarding it (ectal and ental valves of Gage) are seen to flap idly in and out of the opening. 18. The ectal valves may, as claimed by Gage, help to direct the inflowing current of water to the central part of the gill sac, but the writer has obtained no evidence that this is the case, nor does she see any reason to believe that during expiration there is a movement of the water within the gill sac in the definite manner indicated by Gage. 19. In the attached Lampetra wilderi and Ichthyomyzon concolor in normal respiration, the ectal valve of Gage is relaxed, that is, its free edge is not stretched and no other function is observable in it than that of aiding in directing the expired current of water. 20. At the moment when Lampetra wilderi or Ichthyomyzon concolor detaches itself the dorso-ventral axis of the external branchiopores is seen to elongate so that the free border of the ectal valve is stretched taut. The ental valve at the same time strikes against the inner surface of the ectal valve and is thus prevented from turning outward. The external branchiopore is thus closed. 21. The elongation of the dorso-ventral axis of the external branchiopore is due to the contraction of the muscles, the ectal and ental, which act upon the cartilaginous ring to which the valves are attached. 22. If the head of a Lampetra wideri is above the surface of the water, at the moment of detachment, a few drops of water are seen to issue from the oral funnel. If the head of an attached lamprey is far enough above the surface of the water so that two or more branchiopores are exposed, air and water issue from the mouth when the animal detaches itself. If carmine laden water has been introduced into the gill sac of an attached animal the head of which is submerged, a red stream is seen to issue from the mouth at the moment of detachment. 23. It is concluded from 20, 21 and 22, that detachment is effected by a current of water directed forward from the gill sacs through the water tube and pharynx so as to destroy the vacuum in the mouth and oral funnel. 24. If a thin mixture of carmine in water be introduced into the gill sac of a free Lampetra wilderi or I. concolor by means of a pipette held opposite the external branchiopores, the fluid is expelled from the external branchiopores by contraction of the gill sacs somewhat more violent than those of ordinary respiration. 25. If a thick carmine mixture be introduced as under 24 it frequently happens that a violent contraction of the branchial region follows, accompanied by a discharge of the carmine from the mouth. At the moment of this discharge the external branchiopores are seen to be closed as noted under 20. 26. If a stream of thick carmine mixture be directed gently into the oral funnel of a free Lampetra wilderi or Ichthyomyzon concolor so as to fill the funnel, it frequently happens that there is a violent contraction of the branchial sac, accompanied by a stream of water which issues from the mouth and expels the carmine solution. At the same time the external branchiopores are seen to be closed as noted in 20. 27. It is concluded from 25 and 26 that a current of water from the gill sacs forward through the water tube, pharynx and mouth cavities is the agent by means of which these lampreys habitually cleanse pharyngeal and mouth cavities and is the only means by which bodies too large to pass into the alimentary canal or through the branchiopores, may be removed. 28. The current of water directed forward through the mouth, by means of which these lampreys are able to detach themselves and to cleanse the mouth cavity and pharyngeal cavity affords the first adequate explanation of the function of the valves of the external branchiopore, of the water tube and of the velar valve. 29. In the free Ichthyomyzon concolor, by the use of carmine and water, a gentle current may sometimes be seen entering the mouth during the inspiration and passing out through the gills. 30. The teeth of the oral funnel of Petromyzon marinus are so arranged in concentric loops that when moved in radial lines by the action of the annularis muscle they lacerate every part of the surface with which the funnel is in contact. 31. The tongue of the attached Lampetra wilderi or Ichthyomyzon concolor may be thrust forward so as to bring its teeth in contact with the surface of its host and thus when the animal is feeding the lingual teeth aid those of the oral funnel in lacerating the tissue of the host. 32. When the tongue is thrust forward in these attached lampreys so that it no longer serves to maintain the vacuum in the mouth cavity by closing the cavity posteriorly, the semiannularis muscle is believed to contract and thus to maintain the closure of the mouth cavity. In this way the lamprey is enabled to use the tongue in feeding without loosening its hold on its host. 33. After relaxation of the semiannularis muscle the food in the oral hood of the attached lamprey is believed to be pumped into the pharynx by the piston-like action of the tongue working in the mouth cavity and to be forced thence into the œsophagus by the contraction of the muscles of the pharyngeal wall. 34. The intestine of a single specimen of Petromyzon marinus unicolor taken in December from Cayuga Lake, N. Y., was found to contain not only blood but muscle, bone, the gill arch of a small teleost and other tissues, probably those of the host to which the animal had been attached. Gage's ('93) statement that this species feeds only on blood of the host is thus erroneous. 35. In P. marinus, Lampetra wilderi, and Ichyomyzon concolor there projects forward into the pharynx from the cephalic end of the united walls of the œsophagus and water tube a pair of jaw-like structures, the velar jaws. 36. The velar jaws are adjacent to the velar valves which guard the opening from the pharynx into the water tube and the two are supported by a continuous pincer-shaped cartilaginous frame work, actuated by muscles in such a way that closure of the velar valves approximates the velar jaws; while opening of the velar valves separates the velar jaws. 37. When the attached lamprey is feeding, the velar valves close the entrance of the water tube and thus prevent food from entering the water tube and gill sacs. The velar jaws are closed and it is believed passive during this process. 38. The statement made by Günther (1853) and Abbott (1875) to the effect that the free lamprey feeds on fish and eggs or small invertebrates are not supported by the examination of stomach contents. 39. It may be possible for the lamprey to feed when free on minute forms or on somewhat larger animals siezed and held between the approximated halves of the oral funnel. The minute forms or the fragments resulting from the laceration of the larger forms might then be carried to the pharynx by a current of water entering the mouth. 40. If the lamprey feeds when free by means of a current of water entering the mouth it is possible that by a simultaneous closure of velar valves and velar jaws, food particles which would otherwise be swept into the water tube are held between the velar jaws. By the simultaneous opening of the velar valves and velar jaws a current of water from the mouth cavity into the pharynx might carry a food particle from the velar jaws into the open œsophagus. On the other hand, a current of water from the water tube might expel such a food particle through the mouth.