418 



ORGANS OF GENERATION. 



in which the eggs are frequently hatched. 

 Near its termination the oviduct communicates 

 with a glandular apparatus supposed to furnish 

 the viscid envelope by means of which the 

 eggs are generally agglutinated together. 



In the Cephalopoda likewise, as in the Mol- 

 lusca generally, the generative system is single. 

 In this class the testis is an azygos viscus, 

 composed of elongated branched coeca, in- 

 closed in a membranous capsule, into which 

 apparently the seminal fluid escapes. The vas 

 deferens is narrow, and convoluted at first, 

 but afterwards it enlarges and becomes mus- 

 cular in its structure, serving doubtless as an 

 instrument for the expulsion of the semen. 

 This seminal canal receives the duct of a large 

 glandular mass, and dilating into a pouch, 

 ultimately terminates at the root of a rudi- 

 mentary penis, apparently adapted to intro- 

 mission, although it has not yet been ascer- 

 tained whether actual copulation takes place, 

 or whether the ova are fecundated after their 

 extrusion, as is the case with fishes. 



In the female Cephalopoda the ovarium, like 

 the testis of the male, is azygos, and placed 

 in the same situation. Its structure is remark- 

 able, being a strong capsule, to the interior of 

 which adheres a cluster of vesicular bodies 

 denominated ovisacs, from which, at certain 

 seasons, the ova escape. From the ovarian 

 capsule arises the oviduct; this is in some 

 instances a single tube, but in others divides 

 into two canals ; in either case, before its ter- 

 mination behind the base of the syphon, it 

 passes through a thick laminated glandular 

 structure, which secretes the dense coriaceous 

 investment enclosing the ova, and the material 

 which unites them into the racemose clusters in 

 which they are usually found. 



Vertebrata Ovipara. In the vertebrate divi- 

 sion of the animal kingdom the generative 

 system presents great varieties, although from 

 the lower to the higher orders we may distinctly 

 trace a series of gradations which, in a physio- 

 logical point of view, are of the highest interest. 



In Fishes the ovaria are formed upon two 

 distinct types. In the osseous fishes they are 

 for the most part two large membranous sacs, 

 which, when distended, occupy a considerable 

 share of the abdominal cavity ; these open by a 

 short canal in the vicinity of the anus. In these 

 capacious sacs the ova are developed : they are 

 found united together by a delicate membrane, 

 and attached in numerous festoons to the walls 

 of the ovary until sufficiently mature for expul- 

 sion, when, breaking loose from their con- 

 nexions, they escape into the ovarian cavity 

 and are discharged through its excretory duct. 

 In this case the Fallopian tubes found in other 

 vertebrata do not exist, the oviduct being pro- 

 longed from the ovary itself in the same manner 

 as the duct of a secreting gland, and the whole 

 apparatus, in fact, strongly resembles what we 

 have found in the Conchifera and other Mol- 

 lusks, the great distinction consisting in the 

 necessity which here exists for the impregnation 

 of the ova by the agency of the male. The 

 fecundation of the eggs is effected externally, 

 after their expulsion, and, in fact, it is the 



spawn rather than the female, which forms the 

 object of the pursuit of the male, as in most 

 instances both sexes appear as careless con- 

 cerning each other as they are of the off- 

 spring which they produce. The ova, which 

 are incalculably numerous, are deposited in 

 shallow water, where they may receive the 

 influence of the solar beams, and in this situa- 

 tion are eagerly sought after by the males 

 destined to make them fertile ; these, urged 

 apparently by the necessity of ridding them- 

 selves of an inconvenient load, discharge the 

 secretion of their voluminous testes into the 

 water, which, becoming diffused in the vicinity 

 of the ova, is sufficient for their impregnation. 

 In the males of this class of fishes the tesles 

 are of enormous size, equalling in bulk the 

 ovaria of the other sex, and occupying a corres- 

 ponding situation in the abdomen. Each testis 

 is made up of a congeries of seminal canals, 

 which, when inflated through the excretory 

 duct, distend the whole organ. The seminal 

 tubes are in most instances arranged parallel to 

 each other, and are closed at one extremity 

 while the other terminates in the common canal 

 or vas deferens, which in every respect resem- 

 bles the oviduct of the female. 



This is the most usual structure of the male 

 apparatus of fishes, but in some, as in the Shad 

 (Clupea Alosa), the seminiferous tubes form 

 innumerable ramifications and anastomoses in 

 the substance of the testicle, easily discernible 

 by the naked eye ; and from the plexus thus 

 produced coecal tubes are prolonged to the sur- 

 face of the organ, where they terminate by 

 rounded extremities, giving the whole viscus, 

 externally, a granulated appearance. (Fig- 

 204.) 



A few of the osseous fishes form remarkable 

 exceptions to the usual mode of impregnation, 

 the ova of the female being in such fecundated 

 prior to their expulsion by actual copulation 

 with the male ; and in some rare instances, as 

 in the Blennius viviparus, the young are even 

 produced alive, the ova being retained within 

 the oviduct until they are hatched. In such 

 cases the termination of the vas deferens swells 

 into an external projection resembling a rudi- 

 mentary penis, and, indeed, actually performing 

 the office of an organ of intromission. 



In the more highly organized cartilaginous 

 fishes, and even in some osseous genera, the 

 structure of the generative system is entirely 

 different, commencing that type which charac- 

 terizes tiie reproductive organs of all the other 

 vertebrate classes. In these the ovaria are not 

 hollow sacs which have their cavity prolonged 

 to the exterior of the body, but the ova are 

 developed between layers of membrane sus- 

 pended in the abdomen, which are unprovided 

 with any canal immediately communicating 

 with them. Such are the ovaria of the Eel 

 and the Lamprey, which are formed of nume- 

 rous festoons of delicate and vascular membrane 

 suspended in front of the spine. The ova pro- 

 duced between these membranous layers when 

 mature break loose into the cavity of the 

 abdomen, and are discharged through a simple 

 orifice in the neighbourhood of the anus. In 



