352 Vertebrata. 



the eggs in one region, the spermatozoa in another. In not a few others 

 it may be noticed as a quite regular occmrence, that the sexual glands have in 

 some measure a dual character, being, for the most pai-t, either ovary or testis, 

 but having a small portion of the ovary forming a testis, or of the testis foi-ming 

 an ovary. These small portions do not, however, form ripe sexual products. So 

 also, a portion of the testes of the Toad {Bufo) resembles an ovary, but it does not 

 produce ripe ova.* As rare abnormalities, such relations may also obtain in the 

 higher Vertebrata {e.g., in Mammalia) ; for instance, a testis may occur on one 

 side, an ovary on the other ; or the gland of each side may possess in part, the 

 structure of a testis ; in part, that of an ovary : but in this case ripe genital cells 

 of both kinds are apparently not produced. More common than these true 

 hermaphrodites are the so-called pseudo-hermaphrodites, which 

 possess testis or ovary alone, but show the characters of the other sex in the 

 dvicts or the structure of the copulatory organs ; amongst the domestic animals 

 for instance, it is by no means rare to find males which possess very well- 

 developed Miillerian ducts, like those of the female. Certain normal arrange- 

 ments may be regarded as slight indications of pseudo-hermaphroditism ; e.g., 

 the presence of rudimentary Miillerian ducts in the male, which has been 

 already mentioned, or the rudimentary copulatoiy organs in certain females 

 (clitoris of Mammalia, etc.). 



Most Vertebrates are oviparous. The egg, -when laid, is 

 sometimes surrounded by a gelatinous mass (Amphibia) ; iu other 

 cases by a horny shell (Selachii) ; or again, by a tough or brittle 

 calcareous shell (Reptilia, Aves), which encloses, besides the egg-cell, 

 a mass of albumen, which will later be gradually absorbed by the 

 embryo ; all the coverings are secreted by the glands of the oviducts. 

 Many Vertebrata are, however, viviparous, embryonic develop- 

 ment occurring in the oviduct of the mother (or in Teleostei in the 

 hollow ovary). In the simplest cases, the egg, surrounded by 

 the usual coverings (shell, etc.), develops within the body of the 

 parent without the assistance of any additional nourishment ; the 

 ducts of the female simply afford protection to the egg [e.g., in 

 many Reptilia) : ovoviviparous animals. An approach to this 

 condition occurs in many oviparous forms, where the egg when 

 laid contains a more or less fally-developed embryo, the first part 

 of development occurring within the body of the parent, the conclu- 

 sion externally (e.r/., in the common Ringed Snake). In other 

 viviparous animals the embryo lies in, and is nourished by, a fluid, 

 secreted usually by the wall of the oviduct, which it absorbs into the gut 

 or through the skin (Zoarces, some Rays, Marsupials) ; in others, again, 

 processes from the embryo grow into the wall of the oviduct and serve 

 for the absorption of blood from the mother, upon which the foetus 

 is, as it were, parasitic (Mammalia, one Reptile, and Selachians). 



* According to the interpretation of some observers, the Hag (Myxine) is a true 

 hermaphrodite; which is male whilst young, later female. The correctness of 

 this conclusion must still remain doubtful ; certain it is that in some male specimens 

 of this form, the anterior portion of the sexual gland has the character of an unripe 

 ovary, whilst the posterior part constitutes a testis ; but whether this region later 

 develops into a ripe ovary, or whether, like the similar part in the male Toad, it 

 remains in this condition, cannot be deQJded from the investigations so far made, 



