Observations on living growing lymphatics in the tail of the frog larva

Recent studies hare led to a distinct advance in our knowledge of the lymphatic system.Yet there are many points in which this knowledge is still incomplete.The observations here recorded seem to have a bearing upon some of these points, and hence seem worthy of presentation to the Association.The studies were made on liviiig frog 1ai.w; the species used mere Rana sylvatica, R. palustris and R. catesbiana.Two devices were employed, both of which were essential to the success of the observations, an upright chamber and chloretone anesthesia.The former permits observations to be carried on with the larva in its normal upright position.Chloretone serves to keep the larva motionless while under observation.The iisc of chlorctonr introdiices slightly abnormal conditions.Yet by alternating the periods of anesthesia with return to fresh water, the same larva may be kept under observation for several hours daily, for three or four weeka.During this time growth continues, though somewhat retarded.In order to preserve accurate records of the various stages, drawings were made both with and without the aid of the camera lucida.The micrometer eye-piece was employed in making measurements.With the assistance of careful records, little difficulty was esperienced in finding the same structures-blood-vessel, lymphatic, even connective-tissue cell-in successive observations.The fin expansion of the tail of the frog larva, in early stages, is rather opaque, owing to the prcwnce of pigment and yolk granulcs.During this period it is possible to distinguish the course of the blood-vessels only by the moving blood-corpuscles.Gradually this opacity diminishes, until eventually, at lengths which vary for dif-(183).Thc blood-vessels first demand a short description.