226 Dr Martin Barry on (he 



centres being observable in the walls of capillaries (Plate II., 

 fig. 49 d,) which are evidently nuclei of the cells forming those 

 capillaries, it is probable that the walls of capillaries also are 

 germinal membranes, which, by their nucleal orifices, take up 

 and distribute on their exterior the hyaline of the blood-cor- 

 puscles ; this hyaline being then absorbed by other centres 

 for nutrition or the formation of new parts. 



Explanation of the Plates, 

 PLATE I. 



Fig. 33. From ova of the Rabbit. «, Network representing part of the in- 

 cipient umbilical vesicle. A hollow process or little vSac, consisting of incipient 

 cells, having been given off by the rudimental embryo (the nucleus of a cell), 

 those cells coalesce where in contact, and form this network ; which, enlarging, 

 at length lines the ovum. The pellucid nuclisi of the coalesced cells are at the 

 surface of their cells. They are surrounded by minute globules, and have no 

 nucleolus. /S, The same object in a stage more advanced. It now lines the 

 ovum, and the membranous portion of the network is disappearing. A nucle- 

 olus is notv coming into view, y, Stage still more advanced ; — all traces of a net- 

 work have disappeared, and the nuclei alone remain. — (Phil. Trans., 1839. 

 Plates VIII. and VII., Figs. 132, 120, 121.) 



Fig. 34. A later stage of the objects in the preceding figure. Cells have 

 been formed by cy to blasts, arising out of bodies such as those in fig. 33, y. 

 Each cell has a pellucid nucleus, corresponding to that which was the nucleolus 

 in fig. 33, y. And ivhat were nucleoli in jig. 33, y, are notv nuclei. Of these 

 nuclei, there are seen in the figure three stages, «, /3, y, — a exhibiting the l6ast 

 advanced, and y the most forward stage, a, The nucleus is merely a portion 

 of hyaline, not surrounded by any globules, and not having a nucleolus. (■>, 

 Globules are now seen surrounding the nucleus, and in two instances a nucle- 

 olus is coming into view, y, The nucleus is now surrounded by a membrane, 

 formed by globules such as those at /3, and it has now a well-defined nucleolus. 

 —(Phil. Trans., 1839, Plate VIII., fig. 150.) 



Fig. 35. Young blood-coi'puscles of the tadpole of the large Toad of Jersey. 

 They are cytoblasts.— (Phil, Trans., 1841, Plate XX., fig. 74, /3.) 



Pig. 36. Young blood-corpuscles, a of the Leech, and jS of the fa-tal Sheep. 

 Some of the latter are escaping from the parent-cell. — (Phil. Trans,, 1841, 

 Plates XIX. and XXIII.) 



Fig. 37. Blood-red bodies derived from blood-corpuscles of a bird, the Wry- 

 neck (Yunx Torquilla, LiNN.); and forming ova in their ovisacs, a. Originally 

 elliptical, has become round. /3, The outer part consists of cytoblasts, which 

 surround a centi-al cytoblast. y, The central cytoblast has become a cell, the 

 germinal vesicle, and exhibits a distinct orifice in the situation of the future 

 germinal spot. (The entire body y appeared to be membranous at its surface, 

 fi'om the remains of the cell-membrane formed by its cytoblast.) ^, The ger- 

 minal vesicle and its orifice are much larger, i, The germinal vesicle has fur- 



