IN THE BODIES OF ANIMALS. 403 



the uterus and the ovaries to the foetus, have conceived it pos- 

 sible that the ovules are imbibed by the young with the ma- 

 ternal milk. But worms have been observed in the foetus, and 

 cannot therefore have received them from this source. Many 

 infants are entirely deprived of the breast, and if the ovules 

 are communicated to the infant by its mother's milk, the ego-s 

 of all the species must, of necessity, be transferred to the 

 mammae ; the minute structure of the vessels of these organs, 

 as of the uterus, &c. before alluded to, forbids such an 

 event. 



With respect to birds, it was the opinion of Werner that the 

 ovules were communicated to the young by the beaks of their 

 parents ; that the food, after remaining for a certain time in the 

 crop, became saturated with the fluids of the body, and charged 

 with parasitical germs, and that in this way they found a ready 

 entrance into the bodies of the young birds. 



But to this may be objected, that there are many birds who 

 do not feed their young with food laid up in the crop. But, as 

 far as I have observed, those which are furnished with a crop 

 are particularly free from worms, nor have I read any thing to 

 the contrary. And if worms or their eggs are conveyed thither, 

 we should have one or other of the Strongyli among their 

 number ; the eggs of the other worms then arrive at the crop 

 by the same avenues as those by which they reach the uterus 

 and mammae in the Mammalia. 



If this theory be examined in its bearing upon the fishes, 

 the objections will be found still greater. Werner believed that 

 the worms or their ovules would find ready access to the bodies 

 of young fishes, from the fact that they receive their nourish- 

 ment in the same fluid in which the adult fishes deposit their 

 excrement. 



Plausible as this may appear, I believe it to be altogether an 

 unsatisfactory explanation. We must not forget that a very 

 large proportion of the parasitical worms infesting fish do not 

 reside in the intestinal canal, but that they occur either free 

 or enclosed in cysts in the liver, in the abdominal cavity, and 

 in the muscles ; therefore the ovules of these cannot be de- 

 jected with the excrement, and, of consequence, they are not 

 swallowed by the young fish. 



We do not find ourselves extricated from the difficulties, 

 when we turn to the Amphibia and Insecta, for here the eggs 



