THE OVA AND OVARY IN MAN AND OTHER MAMMALIA. 209 



epithelial corpuscles, and the so-called columnar epithelial 

 cells which line the pleuro-peritoneal cavity of the embryo, 

 are nuclei which have a thin film or investment of proto- 

 plasm round them. These nuclei are the homologues of the 

 nuclei of the peritoneal epithelial cells. When a corpuscle 

 divides, each half of the nucleus carries with it a small in- 

 vestment of protoplasm. The protoplasm round the nuclei 

 varies considerably in quantity during the development of 

 the germ epithelial corpuscle. The term cell is employed in 

 somewhat different significations by biologists. Some, for 

 example, holding that a cell must have a definite wall, 

 whilst others look upon the wall as of secondary and minor 

 importance, and hold that a cell essentially consists of a 

 nucleated mass of protoplasm. The germ epithelial cor- 

 puscles and connective tissue corpuscles do not possess a cell 

 wall. When once a cell wall has formed round a corpuscle, 

 the nucleus and cell contents may divide. The cell wall 

 does not participate in the division, but incloses the products 

 of the division. The cell wall may burst and liberate the 

 contents of the cell. 



Every egg cluster is included in a mesh of the stroma. 

 This mesh consists of connective tissue corpuscles and 

 minute blood-vessels whose walls consist of such corpuscles. 

 Delicate processes of this vascular young tissue from the 

 wall of the mesh grow inwards among the corpuscles which 

 are developing into primordial ova. On tearing to pieces 

 small fragments of a seven and a half months' foetal ovary, 

 and placing the debris in a little water under the micro- 

 scope, we find small groups of primordial ova (figs. 7, 8), 

 and single individuals (figs. 9, 10, 11), which have been 

 torn away from the egg cluster, and in connection with 

 some of the largest of these we frequently find fusiform 

 corpuscles (figs. 10, 11, n, n) similar to those which lie in 

 the walls of the meshes. In good specimens the fusiform 

 corpuscles are found laying in indentations in the yelk 

 substance (figs. 10, 11) which surrounds the germinal 

 vesicle of the primordial ovum, and sometimes we see 

 primordial ova whose yelk is indented in many places, but 

 the fusiform corpuscles have been displaced from these 

 indentations. No zona pellucida is found round such young 

 primordial ova. The connective tissue corpuscles must 

 therefore be in contact with the yelk of the primordial ova. 



Directing our attention to the youngest follicles, we find 

 these vary in size, but in every case the young ovum fills up 

 the whole follicle in such a manner that its protoplasm 

 presses against and distends the follicular wall. Little fusi- 



VOL. XVI. NEW SBil. O 



