THE 



AMERICAN NATURALIST 



Vol. XLIII December, 1909 No. 516 



THE CTJTICULA AND SUBCUTICULA OF TRE- 

 MATODES AND CESTODES 

 PROFESSOR HENRY S. PRATT 

 Haverford College 



The membrane which forms the outer covering of the 

 body of trematodes and cestodes and is usually called the 

 euticula differs in certain important particulars from that 

 of other invertebrates, and its morphological significance 

 has long been a matter of dispute. The most noticeable 

 feature of this difference is the apparent lack of a hypo- 

 dermis in these worms, the euticula being bounded on its 

 inner surface by the superficial muscle layers and the 

 parenchyma which fills the body-cavity. 



In the last few years, however, a theory of the euticula, 

 which in the early years of modern helminthology was 

 the prevailing one, has been revived by Professor F. 

 Blochmann (1896), who has presented its claims to recog- 

 nition with so much force and ability that it has been 

 accepted by most helminthologists and zoologists as best 

 accounting for the facts. It has also found its way into 

 some of the best text-books and bids fair to become, in 

 the ordinary course of events, one of the dogmas of 

 science. 



According to this theory, the euticula of trematodes and 

 cestodes is a true euticula morphologically, which is 

 secreted by a hypodermis, as in other invertebrates. This 

 hypodermis, however, has undergone a metamorphosis, 

 for instead of forming a continuous layer of cells situated 

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