EEPEODUCTIVE FUNCTIOHS. 905 



eggs are covered by a horny envelope. In others the fecundated eo-o-s 

 remain in the interior of the oviducts and there develop, and the animal 

 bears its young. 



In reptiles, as in birds, the product of generation comes from the 

 female organs in the state of an egg, while in most cases fecundation 

 precedes, as in the birds, the escape of the egg, and the egg at the time 

 of its exit is contained within a solid envelope, although, as a rule, less 

 resistant than that surrounding the egg of the bird. 



Various batrachians extrude their eggs before fecundation and the 

 male fecundates them while clinging to the body of the female at the 

 moment of their exit. In cases where copulation takes place the exit of 

 the eggs occurs at a considerable interval after their detachment from the 

 ovary, and the egg retained in the oviduct develops and is not expelled 

 until just at the point at which the young is able to carry on a separate 

 existence ; while in some instances, as in some serpents, incubation is 

 terminated and the eggs are ruptured within the body of the female, and 

 the living young are expelled from the body of the mother. Reptiles, as 

 a rule, do not incubate their eggs themselves after extrusion, but they de- 

 posit them in the sand or in the water, as in the case of the amphibious 

 reptiles, where the external heat is sufficient to accomplish their 

 incubation. 



Females of the class of reptiles have two ovaries and two oviducts^ 

 which open scparateby into the cloaca, the oviducts, as in birds and 

 mammals, not being continuous with the ovary, but being free in the 

 abdominal cavity, and possessing trumpet-shaped extremities analogous 

 to the fimbriated extremities of the Fallopian tubes in mammals. 



The male organs of generation differ in different species. In the 

 batrachians there are no organs of copulation. The spermatic canals open 

 into the cloaca, and fecundation occurs, as in the birds, by the application 

 of the ani, when fecundation precedes the expulsion of the eggs. In other 

 groups of reptiles a penis is present, into which the spermatic canals 

 open. 



Of all the reptiles batrachians are the most productive. Turtles 

 extrude four to five eggs, serpents ten to twenty, and frogs many hun- 

 dreds. After escaping from the egg batrachians are not, as a rule, fully 

 developed, but during the first two weeks undergo a true metamorphosis, 

 first existing in the form of tadpoles, deprived of limbs, but having a 

 tail and breathing by branchia situated at the side of the neck. Grad- 

 ually limbs develop and the tail as well as the gills disappear, and the 

 animal then breathes by lungs. 



In birds the product of generation leaves the sexnal organs of the 

 female while still within the egg, and such animals are, therefore, termed 

 oviparous, although it must not be forgotten that man and other animals 



