DEVELOPMENT OF LYMPHATICS. 



105 



for a short distance down one such filament in connection with a vessel, and 

 then observed to cease abruptly at a part where the filament becomes imper- 

 meable, and this apparently not from collapse of its walls, but either from no 

 tubular cavity at all, or only an exceedingly narrow one, having yet been de- 

 veloped in its fine thread-like structure. In other instances isolated parts 

 along the course of the fine filaments appear first to have become hollow, 

 for here and there are observed isolated groups of coloured nucleated 

 blood-corpuscles in distended parts of the narrowest tubes (a a, fig. 23). 

 This circumstance would seem to prove that just 

 as the heart and first blood-vessels are developed 

 independently of each other, so may perfect blood- 

 corpuscles be developed in parts not in immediate 

 connection with the already formed vascular 

 system, and from other materials than those de- 

 rived directly from the contents of the blood-ves- 

 sels ; for in several of the instances in which the 

 above peculiarity was observed, the part con- 

 taining corpuscles was connected at either ex- 

 tremity with a blood-vessel or an elongated cell 

 only by an exceedingly fine filament, which ap- 

 peared quite incapable of transmitting a particle 

 of even much less size than a blood-corpuscle. 

 The walls of the fine tubes, as was observed by 

 Kolliker, appear to be formed of the membrane 

 of the cell which is drawn out into the elongating filaments proceeding 

 from these bodies : in structure it appears quite homogeneous. The 

 large vessels possess delicate membranous walls with a fine, longitudi- 

 nally fibrous structure, and, as noticed by Kolliker, with scattered nuclei 

 imbedded in their substance.* 



Development of Lymphatics. The mode of development of lymphatic 

 vessels, which has hitherto been involved in complete obscurity, appears 

 to be now fully elucidated by the researches of Kolliker on the forma- 

 tion of the tissues in young Batrachians.f This laborious investigator 

 has found that these vessels are developed in a manner almost precisely 

 similar to that pursued in the development of blood-vessels, namely, by 

 the junction and fusion of processes from star-shaped cells with each 

 other, or with off-shoots proceeding from already formed vessels. The 

 chief point in which the development of lymphatics differs from that of 

 blood-vessels, is in the processes from the cells, and from already formed 

 vessels, uniting directly with each other, and thus producing a tube which 

 does not give off lateral communications so as to form a network ; for the 



* The chief interest of the above observations is in their proving that the blood-vessels in 

 Mammalia are developed after a plan exactly similar to that observed by Kolliker in Reptiles, 

 t An. des Sc. Nat. 1846, p. 99. 



