ANDROCiVNOUS ANIMALS. 



of laying. This is a case somewhat analogous to those 

 quadrupeds which produce several young at a birth with 

 one impregnation, differing, however, in the circumstance 

 that the eggs are not all produced at the same time, al- 

 though they are afterwards hatched by the same incubation. 

 In the aphides -, or plantJice, as they are called, one im- 

 pregnation not only renders fertile the eggs of the indivi- 

 dual, but the animals produced from these, and the eggs 

 of those again, unto the ninth generation*. 



III. ANDROGYNOUS ANIMALS. 



The structure of the reproductive system in those ani- 

 mals which have the sexes united in the same individual, 

 exhibits two distinct modifications. In the first, impregna- 

 tion can only be effected by the union of two individuals. 

 In the second, the hermaphroditism is complete, and im- 

 pregnation takes place without any assistance. 



1. In nearly all those androgynous animals, where there 

 is sexual union, the testicle is single, there is an external 

 penis, and the opening for the escape of the spermatic 

 fluid is situated at its base. The ovarium is also single. 

 The external openings of both organs are uniformly situat- 

 ed on one side of the body. In some cases, they terminate 

 in a common cavity, while, in others, the openings of the 

 male and female organs are removed to some distance from 

 each other. 



Impregnation, in the animals now under consideration, 

 takes place internally, by the mutual application of the 

 sexual organs of two individuals. The eggs, in a few spe- 

 cies, are retained until hatched ; but, in general, they are 



* " Observations on the Aphides of LtNN-Sua," by Dr WM. RICHARDSON, 

 Phil. Trans. 1771, p. 182194, 



