2G8 ANIMAL PARASITES. 



without through the skin into other animals (especially aquatic 

 mollusca and insects, and perhaps also other higher animals which 

 occasionally visit standing water), so as to get from thence into 

 higher animals, where the Trematoda finally become mature. 

 The account to be given hereafter of Distomum hepaticum in the 

 sole of a man's foot, makes it appear very probable that even 

 D. hepaticum is one of those species which pass through a Cercaria- 

 form and bore through the skin of other creatures with loss of 

 the tail. However, I do not hesitate to call the specimen of 

 D. hepaticum here referred to an individual which had got into 

 an unsuitable place. The second tailless form of the young 

 Trematoda above mentioned appears to get at once, and whilst 

 enclosed in the nurse, into the intestine of higher animals with- 

 out any active migration. Although, up to the year 1855 there was 

 no certain evidence of the mode of transformation of these young 

 Trematoda, yet, after the great discovery of Steenstrup, it was not 

 difficult to conjecture that sheep, rabbits, men, &c, might infect 

 themselves with D. hepaticum by their devouring small mollusca 

 inhabited by the brood of the Distomum in question, which were 

 living upon the grass of the meadows, or by swallowing small 

 aquatic mollusca, or free broods of Distomum, when drinking 

 from stagnant, marshy waters. As a matter of course, the pos- 

 sibility of this mode of infection was stated openly by public 

 teachers of the veterinary art and of zoology, and also by myself 

 in lectures to the agricultural societies of my native country, 

 although I received epistolary correction for this idea from one 

 of the first German helminthologists. But the priority could not 

 have been ascribed to any one but Steenstrup himself; and neither 

 Leuckart, Haubner, nor myself, nor others will claim any priority 

 in this respect. According to Gerlach, the eggs of D. hepaticum 

 were administered to lambs without result, and from this, it 

 appeared clearly that a further development of the eggs of 

 Distoma passing out with the dung of the sheep, exterior to the 

 body of the sheep, is necessary. 



An essential proof of the truth of these views regarding the 

 production of D. hepaticum has been furnished by De la Valette 

 St. George. In his Inaugural Dissertation, which is adorned 

 with two admirably executed plates and is entitled ' Symbolae ad 

 Trematodum evolutionis historiam ' (Berlin, 1855), De la Valette 

 enlarges upon the developmental history of the Trematoda. In 

 the embryos of a Distomum from the intestine of Sterna Cantiana, 



