4 C. S. MINOT ON DISTOMUM 



ing the Cestods in this respect, though in the Trematods I have examined I found no deep 

 muscular coat which so characteristically separates the " Mittelschicht " from the " Rinden- 

 schicht" (cf. Leuckart, Parasiten) in segmented tape worms. 



From these observations, it will be seen that the muscular system of Distomum resem- 

 bles that of the Cestods more closely than it does that of the Planarians. But the exist- 

 ence of the single row of external longitudinal muscular fibres should be especially noted 

 as bearing upon the homologies of the muscular layers of Plathelminths. This subject 

 has been discussed in my paper (see above) in Semper's Arbeiten. It also overthrows, 

 beyond all question, Schneider's 1 attempt to classify worms according to their muscular 

 systems, because some species of Taenia clo, and others do not, have the external longitudi- 

 nal layer, and it is evident that orders and classes cannot be founded upon characters that 

 are not constant within the limits of one genus. 2 



The parynchym in my preparations appears as a meshwork of granular protoplasm, with 

 a few oval nuclei imbedded in it. The cavities of the meshwork are more or less rounded 

 in outline. This appearance is well known, but has been variously interpreted. Walter 3 

 believed that there was a series of intercommunicating cavities, fornied by a reticulated 

 connective tissue ; the cells of which consisted of a central area of protoplasm enclosing 

 the nucleus and sending out processes which united with those of the neighboring cells, 

 very much as in the embryonic connective tissue of Vertebrates. Leuckart, 4 on the other 

 hand, asserts that the whole consists of cells, there being no real cavities ; that appearance 

 being produced by the cells containing a large amount of clear fluid, while the granular 

 protoplasm is collected together with the nucleus against the membrane at one j>ole of the 

 cell, similarly to the characteristic cells of the Chorda dorsalis of Vertebrates. If Leuck- 

 art's view is correct, good preparations must show a curved outline passing near the nu- 

 cleus, and there must be also as many nuelei as there are distinct rounded cavities, since 

 each of these is a cell. I have been unable to observe such an appearance, but, on the 

 contrary, I have often seen such stellate cells as were described by Walter. In Caryopkyl- 

 laeus, we find that the meshwork is very fine, the spaces being much more numerous than 

 the nuclei, though of about the same size ; if, therefore, Leuckart's view is correct, it would 

 be necessary to explain this discrepancy between the number of the nuclei and of the 

 spaces he calls cells ; at present I do not see how this is possible. In the segmented Ces- 

 tods the parenchym contains numerous pale, oval cells, without any processes, besides a 

 few stellate cells. I am not certain of there being any corresponding cells of rounded 

 shape in the basal tissue of the flukes. Both kinds are found in the Pharyngocoela, 

 as I have stated in my paper in Semper's Arbeiten, and they will probably be de- 

 tected in the Trematods, when properly searched for, thus adding a new minute homology 

 within the class of the Plathelminths. I may add that Salensky 5 agrees in his description 



1 Anton Schneider. Untersuchungen iiber Platthelmin- 8 Walter. Beitriige zur Anatomie einzelner Trematoden. 

 then. Giessen. 1873. Archiv f. Naturgesch., 1858. Theil I, p. 287. 



2 Huxley, in his recently published Manual of the Anat- * Leuckart. Menschl. Parasiten. Bd. I, p. 457-458. 

 oray of Invertebrates (Araer. ed., p. 172), repeats the cur- 6 Salensky. Amphilina. Zeitschr. wiss. Zool., xxiv, 

 rent statement that the circular coat is external. Of course p, 303. 



this statement requires modification to accord with recent 

 observations. 



