386 



MANUAL OF HISTOLOGY. 



also, namely, the tail of the tadpole. Here (fig. 384) a rapid formation of 

 capillaries, from some already present, may be observed to take place, as 

 has long been known, by a species of budding. 



Fig. 385. From the vitreus humour of the foetal calf. Two vessels connected by a " cord " of proto- 

 plasm, and clothed with an adventitia. a, insertion of this cord into the primary wall of the vessels. 



From the walls of already formed capillaries protoplasm is supplied 

 capable of further independent development (p, p). By the growth of 



this those sprouts and threads 

 are produced to which we 

 have just alluded. These, 

 again, are converted into cords 

 by fusion one with another, 

 and the axial portion of each 



,OW \\ Mb >h-<3M thread becoming fluid subse- 



quently, tubes of protoplasm 

 are formed. 



But with this further trans- 

 formation of the walls a for- 

 mation of new nuclei goes 

 hand in hand. The latter 

 are at first small and not 

 sharply defined, but become 

 larger and more distinct later 

 on. From these two consti- 

 tuents, then, nuclei and pro- 

 toplasm, the vascular or en- 

 dothelium cells already men- 

 tioned are formed by a species 

 of segmentation (Arnold). 



In fig. 385 we have repre- 

 sented something similar in 

 the formation of vessels in 

 the corpus vitreum of the 

 foetal calf. Here, however, numerous adventitial cells are also present. 



The next woodcut also (fig. 386), which appeared in the first edition of 

 this work, represents the same thing. 



Fig. 38(5. Vessels from the tnembrana capsulo-pupillaris of 

 an embryonic pig, 2 inches long, overlaid with round 

 adventitial cells. 1, a fine vessel with a single one of 

 the latter; 2, with numbers of the same; 3, three vessels. 

 a, 6, connected by a transverse thread; 4, clothing of 

 cells only on the undermost portion; 5, a vessel with 

 rounded cells 6, connected by a transverse branch a 

 (which acquires to the right at c, a new clothing of cells) 

 with another tube d, which shows the adventitial cells in 

 profile. 



