39f) ON THE ORIGIN OF ENTOZOA 



when, to my surprise, the stomach contained only one Ascaris, 

 and that a small one, and the small intestines only a few pieces 

 of Tcen'ice. I should have mentioned, that the excrement of the 

 kittens in the box presented occasionally pieces of TcRnta. 

 The results of this experiment were so far satisfactory as that 

 they made known the very early period at which cats become 

 the subjects of worms, but no farther, since they were not 

 direct proofs of the cognate origin of parasitical animals; 

 indeed, the fact of my having detected none in the first animal, 

 and six worms, besides fragments of others in the fourth, went 

 rather to favour that view which regards intestinal worms as of 

 external origin. It then struck me that if their existence in 

 foetal animals could be determined beyond a doubt, that the 

 inquiry would then be brought within somewhat narrower 

 limits, and that the question of their external origin would be 

 set at rest. I had not an opportunity of pursuing the subject 

 till the following autumn and winter, when I had frequent 

 opportunities of examining foetal lambs in the Whitechapel 

 slaughterhouses : here, in several instances, I found the fluke, 

 of no mean size, in the biliary tubes. I have since found, on 

 referring to the excellent helminthological work of Rudolphi, 

 that he notices the same thing as having been observed by Pal- 

 las, but adds, that the observation requires confirmation, seeing 

 that many inorganic substances, concrete mucus, albuminous 

 flukes, &c. have been confounded with worms, an insinuation 

 which, by the by, Pallas ill deserves. Having convinced 

 myself of the cognate origin of parasitical animals in the Mam- 

 i»aUa, I determined to embrace the first opportunity which 

 should occur of examining the intestines of birds in ovo. In 

 the following spring such an opportunity presented itself, and 

 the thrush was the subject. It may be well to mention, that 

 the thrush aflTords " a house and home" to at least three species 

 of worms ; viz. Distoma mesostomum, Tarda angulata, and 

 Ascaris lancea ; the two latter I have often found in the adult 

 thrush, and my object now was to look for them in the bird in 

 ovo. The nest of a thrush, accessible to observation, was easily 

 found. During the first few days I contented myself with ex- 

 amining the nest occasionally only, but for some days previous 

 to the time at which I hoped they would break the shell, I 

 watched them more narrowly, and on examining the nest one 

 morning found one of the birds just liberated from its prison. 



