424 PHILOSOPHY OF ZOOLOGY. 
excluded a short time after impregnation. Even without 
being impregnated, the female organs can- produce eggs 
sumilar 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 Lymnezi 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, im 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. Gemmiparous 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 
