.589 



CHAPTER XIL 



GENERATIVE TKODUCTS AND DEVELOPEMENT OF 

 H^EMATOCRYA. 



The functions of the above-described Generative Organs are 

 ' semination,' ' ovulation,' ' fecundation,' and ' exclusion,' to which 

 is added, in some Ha3matocrya, that of ' foetation.' Semination, 

 or the production of sperm-cells, is peculiar to the testis ; ovula- 

 tion, or the production of germ-cells and vitellus, is peculiar to 

 the ovary : fecundation is the combined act of the male and 

 female. A part of the oviduct is usually modified to add 

 accessory parts to the ovum, or in subserviency to foetation in the 

 viviparous Htematocrya : but, in a few instances, the protective 

 and portative functions are relegated to tegumentary wombs or 

 marsujna, whichmay be developed in either sex. Exclusion of the 

 male generative product is called ' emission,' that of the female 

 generative product ' oviposition : ' but if the ovum be arrested for 

 the process of foetation, the exclusion of the foetus is then termed 

 ' birth.' Sometimes the male assists in the process of exclusion. 



§ 111. Semination of Hamatocrya. — The product of the testis 

 in Fishes consists of ' sperm-cells,' ' spermatoa,' and 'spermatozoa,' 

 with very scanty fluid medium of suspension : the function is 

 seasonal, and attended by 

 rapid increase of the glands. 

 This is greatest in Osseous 

 Fishes, in the testes of which, 

 at the besinning of their 

 enlargement, the sperm-cells 

 (cysts or 'mother-cells') are 

 seen, fig. 399, a, containing sri-rm-i-eiiswitusrenrntuii, Brea.u. recvi. 



one or more spermatoa (' cells 



of developement '), ib. b. These usually escape from the sperm-cell 

 as such, and then undergo some change of shape, through the deve- 

 lopement of the spermatozoa within them. The rupture of the 

 spennatoon gives issue to the extremely fine capillary appendage, 

 or ' tail,' the movements of which extricate the nuclear mass forming 

 the so-called ' body ' of the spermatozoon. In most Osseous 



399 



