STUDIES ON THE ECTOPAEASITIC TEEMATOPES OF JAPAN. ^5 



ranitra, Wright and Macallum'^ hold that the greater part of the 

 digestive process is effected by the fluid content of the intestine, which 

 they think is of an acid reaction. This they infer from their observa- 

 tion that the swallowed epithelial cells of the host have the form of 

 their nuclear chromatia preserved for a long time, which would not 

 be the case were the intestinal fluid of an alkaline reaction. These 

 writers seem to hold also that the secretion of the digestive enzyme and 

 the ingestion of food granules — which they concede to take place to 

 some limited extent — are effected by one and the same cells. Now, 

 remembering that even so low in the scale of life as in Hydra ^^ the 

 cells of the endoderm are differentiated into two kinds, the secretory 

 and the absorptive, it would seem to many very improbable that these 

 two processes should be carried on in the Trematodes by one and the 

 same cells. Confining our attention to the ectoparasitic Trematodes, 

 we see that in all those forms which have the intestine of the first 

 type, viz., that iii which the epithelium is discontinuous, and the cells 

 contain numerous pigment granules, the salivary glands are totally 

 absent ; while in those which have the intestine of the other type they 

 are well developed. Considering this fact in conjunction with the 

 view that the pigment granules of the intestinal cells of the first type 

 ai-e of a zymogenic nature, the thought suggests itself whether the 

 pigment cells of the intestine and the salivary glands are not, in the 

 ectoparasitic Trematodes, vicarious in their functions ; and there seems 

 to be no fact, at least for the time being, that is obnoxious to this assump- 

 tion. In the Planoceridce the so-called salivary glands secrete only a 

 sticky fluid, hence the necessity of secretory cells in the intestine. In 

 the Ehahdqeodida, in some of which the salivary glands are, as already 



1). Wright and Maoallum— Sphyranura Osleri. Journ. of Morphology. Vol. 1, 1887 .pp. 33, 35. 



2). Cf. Grreenwood — On Digestion in Hydra; with Some Observations on the Structure 

 of the Endoderm (Journ. of Physiology, vol. IX, 1888, p. 317—344) and Nussbaum— TJeber die 

 Teilbarkeit der lebendigen Materia (Arch, f, mik. Anat., Bd. 29, 1887, p. 265-3H6). 



