ciiAr. viii.] OEGANS OF RESPIRATION AND SECRETION. 251 



coutalned, must also be reckoned as a part of its function. Tlio 

 development of ripe ova — or oruhdlon — "begins to take place in the 

 first year of the animal's life, and is thenceforth continued till the 

 bodily decay of age sets in. 



It takes place at frequent intervals,* and culminates in the 

 rupture of one or more Graafian vesicles, with the discharge of the 

 (j"\'um or ova from the surface of the ovary through its peritoneal 

 coat into the peritoneal cavity. This process is generally accompanied 

 Avitli more or less constitutional disturbance, and an increased 

 supply of blood to the generative organs. By a wonderful and 

 quite unexplained process of reflex action, the rupture of a Graafian 

 vesicle is accompanied by a spontaneous application of the fimbriated 

 end of the Fallopian tube to the place of rupture. In this way the 

 discharged ovum, instead of being cast loose into the peritoneal 

 cavity, is received into the mouth and canal of the Fallopian tube, 

 and so conve3'ed onwards, by its ciliated lining, to the cavity of the 

 uterus. The walls of the ruptured Graafian vesicle then increase in 

 substance, and thus give rise, for a time, to a yellowish mass termed 

 the corpus liiteum (Fig. 118, i^'). 



Simultaneously with the constitutional disturbance just referred 

 to, the sexual appetite is inflamed, and the animal becomes " at 

 heat." 



The formation of the ova, unlike that of the spermatozoa, does not 

 take place in distinct tubes,t but in the seemingly non-tubular 

 substance or stroma of the ovary. The process of the formation of 

 the ova is so different from that of spermatozoa, and is so closely 

 connected with embryonic conditions, that its description is more in 

 place under the head of development. Nevertheless it may bo here 

 (.)bserved that each ovum is a modified and enlarged cell of the 

 epithelial tissue of the ovary, which is thus, as before pointed out, 

 not the equivalent of a spermatozoon, but of a "sperm-cell" or 

 " spermospore," which is the parent of various spermatozoa. The 

 incipient ovum — or ovigerm — becomes surrounded by other smaller 

 cells, which subsequently, by multiplication and separation form 

 both the "tunica "-ranulosa" of the ovum and the "membrana 

 granulosa " lining the Graafian follicles — fluid gradually formmg 

 and greatly increasing between these at first closely juxtaposed 

 layers. The outer envelope of the Graafian follicle appears to be 

 formed by other epithelial cells, and by a special growth of the 

 ovarian stroma around the developing ovum. 



* It is difficult to ascertain liow often, ! settled; tut the wide divergence of form 



.IS the adult uuimpregnated female cat which exists between the mature sexual 



often seems to be almost continually glands of the two sexes is manifest and 



ready for reproductive activity. indisputable. For some recent observa- 



f Whether the composition of the tions made with reference to this obscure 



ovary and the ionnation ot ova are ! (luestiou, see a paper by ilr. E. A. 



essentially "tubular," is a question Hchiifer, F.E.S., in Pro. Eoy. Society, 



which cannot yet be regarded as hnally ISSO, p. 'lio. 



