292 LECTURE XII. 



fi-om the Internal surface of the dilated part ot the oviduct. Professor 

 Miiller has well described the corresponding foetal cotyledons which 

 are developed from the vitellicle of the embryo. 



In reviewing the various forms of the Generative Oi'gans of Fishes, 

 we find that they resolve themselves into four well-marked grades of 

 complexity. First, reduced to the essential gland, the testis, or the 

 ovarium, without excretory canal. Secondly, with a simple duct, 

 continuous with testis or ovarium. Thirdly, a partial oviduct, as in 

 the Sturgeon, not continuous with the ovarium, and not separated 

 from the ureter. Fourth, a more compact form of testis and ovarium, 

 with a long and complex duct, distinct from the ureter ; the beginning 

 of the vas deferens convoluted into an epididymis and its end dilated 

 into a seminal reservoir, with a plicated glandular inner surface ; the 

 oviduct presenting a nidamental gland near its commencement and 

 dilating into an interior receptacle, with a plicated surface at its ter- 

 minal half Besides the 'claspers' of the Plagiostomes, there are 

 other accessory organs of generation ; viz. the subcaudal marsupial 

 tegumentary folds in the male of some species of Syngnathus 

 (preps. 3226 — 3228), and the sub-abdominal marsupial pouch in the 

 male Hippocamps (preps. Nos. 3230 and 3231). 



DEVELOP31ENT OF FISHES. 



This, the most intricate and difficult, but the most interesting part 

 of the physiology of fishes, is divided, as in other animals, into seven 

 distinct processes: — 1. Seminatiott, or the development of the im- 

 pregnating corpuscles called seminal animalcules, or 'spermatozoa :' — 

 2. Germination, or the development of the germ or ovum susceptible 

 of impregnation : — 3. Fecundation, or the act of impregnation, which 

 is sometimes, though rarely in the present class, accompanied by 

 intromission: — 4. Fcetation, or development of the embryo within 

 the ovum or uterus : — 5. Extrication, or escape of the embryo from 

 the ovum : — 6. Exclusion, or expulsion of the generative product 

 from the parent: — 7. Gr-oicth, or development from the period of 

 exclusion, or of extrication from a previously excluded ovum, to 

 maturity. 



Exclusion of the male generative product is called ' emission ;' that 

 of the female generative product, ' oviposition ;' that of the previously 

 extricated embryo, 'birth:' but these are modifications of the same 

 essential process. The stages of development do not succeed each 

 other as here enumerated, in all fishes : in the Dermopteri and most 

 osseous fishes 'exclusion' precedes 'fecundation,' 'fcetation,' and 

 ' extrication.' In a few osseous fishes and a larger proportion of 

 the Plagiostomes, ' fecundation,' ' foetation,' and ' extrication ' precede 



