424 PHILOSOPHY OF ZOOLOGY. 



excluded a short time after impregnation. Even without 

 being impregnated, the female organs can produce eggs 

 similar in size and appearance to the perfect ones, but 

 which, as possessing no vitality, soon go into decay. This 

 we have often witnessed, when a single individual of one of 

 the Lymnsei has been confined in a vessel of water. 



Examples of this condition of the reproductive system 

 do not occur in any of the tribes of vertebral animals. 

 They are, however, very common among the mollusca, 

 particularly in the pulmoniferous gasteropoda, as the snail 

 and slug. 



2. In those androgynous animals where the hermaphro- 

 ditism is complete, the male organs have not been satisfac- 

 torily ascertained. During the season of conception, the 

 ovarium is replete with a milky fluid, which is probably 

 the sperm, and which has been conjectured to proceed 

 from a testicle concealed by being incorporated with the 

 ovarium. 



The eggs, in some cases, are ejected from the body pre- 

 viously to their being hatched, while, in others, they are 

 hatched internally. In these last, as among the Mollusca 

 conchifera, the young are sometimes found in the gills, 

 into which they have escaped from the ovarium. 



Examples of this structure of the reproductive system 

 occur in the whole of the molluscous animals belonging to 

 the classes Conchifera and Tunicata. 



IV. GEMMIPAHOUS ANIMALS. 



In the reproductive systems, which we have hitherto been 

 considering, sexual organs could be distinctly perceived. 

 In those to which our attention is now to be directed, nei- 

 ther male nor female organs can be detected. No separate 

 act of impregnation is required ; but the young are pro- 

 duced by buds forming on the surface of the body, and 



