336 H. S. DAVIS 



the cells (fig. 21). On being transferred to a slide they become 

 actively motile, often sending out pseudopodia in several direc- 

 tions at once, and soon became very irregular in shape. 



The ectoplasm is easily distinguished as a homogeneous, hya- 

 line layer surrounding the endoplasm which is filled with rather 

 indistinct vacuoles (fig. 1), separated from each other by a denser, 

 homogeneous substance which has much the same appearance as 

 the surrounding ectoplasm. In fact the endoplasm gradually 

 merges into the ectoplasm by the vacuoles gradually becoming 

 less abundant until in the latter they entirely disappear. Usually 

 the endoplasm also contains a few yellowish, refractive globules, 

 evidently composed of fat since they stain intensely with Sudan 

 III. These globules vary considerably in size and numbers, 

 being, in general, more abundant in older individuals; although 

 there is considerable variation in this respect in trophozoites of 

 approximately the same age. In some cases, even in full grown 

 individuals, there are only a few fat globules present while in 

 others they may be very abundant. 



Occasionally the endoplasm contains one or more erythrocytes 

 which are evidently obtained from the blood of the host and are 

 ingested by the parasites (fig. 2). I am convinced that the 

 erythrocytes are actually taken in and digested by the tropho- 

 zoites since I have often found individuals, both in fresh and 

 preserved material, in which they were unquestionably in- 

 closed in the endoplasm. Erythrocytes in various stages of dis- 

 integration occasionally occur within the endoplasm so there 

 can be little doubt that this species actually utilizes solid food. 

 Cohn ('96) found that erythrocytes were ingested by Myxidium 

 lieberkuhni Biitschli, a parasite of the urinary bladder of the 

 pike, but his statements have been questioned by later writers. 

 The evidence in the case of S. dimorpha is, however, so clear 

 that there can be little doubt that this species forms a notable 

 exception, as regards the character of its food, to most of the 

 Myxosporidia. On the other hand, individuals containing ery- 

 throcytes are too few to justify the conclusion that this is the 

 only means of obtaining food. In all probability they absorb 



