364 H. s. PRATT, 



of subrauscular cells usually present. Ou his own part, while he agrees 

 with Brandes iu holding that the cuticula arises as a secretion, Looss 

 (1893, p. 3 and 33) maintains that it is secreted by the entire body 

 of the parenchyma. He says "Ich fasse die Trematodeuhaut als ein 

 Absonderungsproduct auf. Die Bildung der Haut geht in der Haupt- 

 sache vom Körperparenchym aus. Man kann sich jedenfalls vorstellen, 

 dass bei der Umwandlung der indifferenten in die blasig aufgetriebenen 

 Parenchymzellen ein Stoff gebildet wird, der, äusserlich unsichtbar an 

 der Oberfläche angelangt, in die zähflüssige Cuticularsubstanz sich ver- 

 dickt." NicKERSON (1894) agrees fully with Looss and adds several 

 important observations which tend to confirm his theory. Blochmann 

 (1896), the latest writer on this subject, finds beneath the cuticula an 

 epithelium which secretes it. This epithelium, however, although mor- 

 phologically the hypodermis, does not constitute a continuous cell-layer 

 in close juxtaposition with the cuticula, but has suffered a change of 

 position. The superficial muscle-layers have interposed themselves be- 

 tween it and its cuticula, and its constituent cells have at the same 

 time become separated from one another, with the result that the cells 

 have come to lie back in the parenchyma, isolated as regards one 

 another, and joined with the cuticula by long ducts. 



It is quite evident that Blochmann, as Brandes, is giving a new 

 interpretation of the submuscular cells, and it is of great interest and 

 importance that he has demonstrated the presence of ducts connecting 

 these cells with the cuticula with such clearness, and thus confirmed 

 Brandes and proved the undoubted relation existing between these 

 two structures. It seems to me, however, that his theory is open to 

 the same objections which are made above to that of Brandes: if the 

 submuscular cells are a hypodermis what secrets the appendicular 

 cuticula which has none beneath it? Another objection which occurs 

 to me its the following: the epithelial, integumentary covering of the 

 Cercaria is almost invariably shed in Trematodes; if the adult worm 

 possesses a hypodermis, as Blochmann claims, it must be of other 

 than ectodermal origin. 



In my own opinion the explanation suggested by Looss and 

 quoted above, but before him by Leuckart (1886 a, p. 387) comes very 

 near the truth. The cuticula of Trematodes constitutes the peripheral 

 portion of the body -parenchyma of the worm, and is constantly 

 being reinforced by additions over its entire inner surface. I do not, 

 however, find Looss' ingenious hypothesis of the exact manner in which 

 it is formed from the parenchyma, necessary. He supposes a cambium- 



