THE TREMATODA. 97 



but the fact is now as generally recognized, as it is readily 

 proved. 



Thus it is not at all wonderful that I should also have 

 found numerous trematode animalcules in the eyes of 

 om- fresh-water fishes ; but it was very instructive that I 

 should meet with two of these trematode forms in the 

 eyes of thej)ike emd perch, which differed in size and ap- 

 pearance, but nevertheless were so much alike externally 

 and internally, that I could scarcely doubt that they 

 belonged to the same species, and that the one was 

 an earlier condition of the other ; besides these, I found 

 sometimes in the same, sometimes in other eyes, situate 

 here and there, minute watch-glass-shaped capsules, 

 which inclosed trematode animalcules resembling both 

 forms, but especially the larger, and examination soon 

 rendered it certain that this was the pujpa state, inter- 

 vening between the two forms noticed. This interested 

 me so much the more, that I sometimes found these 

 pujpcB on the internal surface of the cornea, and at the 

 same time noticed a finely granular, unorganized streak, 

 which passing through the cornea to the pupa clearly in- 

 dicated the way by which the animal had penetrated 

 previous to becoming a pupa. That these animals had 

 entered from without, was shown also by some pupa 

 which were situated in the skin around the eye, or a little 

 beneath it, or even on the muscles of the globe, (and in 

 this situation, the pup(B doubtless correspond with the 

 encysted parasites, whose occurrence on the muscles is 

 mentioned by Prof. J. Müller, in his memoir on the 

 Psorospermata.) 



I was surprised that I could not recollect, that 

 Nordmann had remarked this form of development, but 

 when I afterwards obtained his celebrated work,* I saw 

 that he was well acquainted with, and had described and 

 figured it all, but only that this interconnexion between 

 them was unknown to him. Two of the forms, for in- 



* A. V. Nordmami, Mikrographisclie Beiträge zur Naturgescliichte der 

 wirbellosen Thicre. Berlin, 1832, 4to. 



7 



