1902.] NATURAL SCIENCES OF PHILADELPHIA. 7 



(1901, p. 149) says: " although very improbable at first sight, it 

 is the only one thus far that fits the case." Wasielewski (1896, 

 p. 22) rejects it, while Delage et Herouard (1896, footnote on p. 

 261) say: " Pour bizarre qu'elle paraisse, il faut bien 1' accepter 

 jusqu'a nouvel ordre, car elle repose sur des faits observes et on 

 n'en connait aucun autre a lui substituer." 



Schaudinn (1900) and Siedlecki (1899) are credited with having 

 confirmed Schewiakoff, the former by Lang (1901, p. 128) and the 

 latter by Calkms (1901, p. 149).' Schaudmn (pp. 222-224) gives 

 data which show that the sporozoites and merozoites of Coccidium 

 schubergii extrude fibres of a gelatinous substance. These fibres 

 carry backward such small particles as may be in the immediate 

 vicinity of the coccidians, and form a trail behind them. In so 

 far as the extrusion of a gelatinous substance is concerned, Schau- 

 dinn' s observations im questionably confirm those of Schewiakoff, 

 but, as will be seen later, they do not necessarily show that this 

 gelatinous substance is the cause of progression. 



Siedlecki (1899, p. 521) says: " Es liisst sich aber bei Mono- 

 cystis aseidue leicht noch ein anderer Bewegungsmodus beobachten : 

 ohne irgendwie ihre GestaUt zu wechselii gleitet sie namlich plotzlich 

 vorAviirts. Die Ui'sache der Bewegung liegt, wie es Schewiakoff 

 fiir andere Gregarinen beschriebeu hat, in einer plotzlichen Aus- 

 scheidimg von Schleim aus dem Hinterende des Korpers, und es ist 

 leicht festzustellen, wie das Tliier durch einen aus ihm plotzlich 

 herauswachsenden Schleimfaden vorwiirts geschoben wird." This 

 can scarcely be regarded as a confirmation of Schewiakoff. 



III. Observations. 



1. As a necessary preliminary, attention is here called to two 

 points of considerable importance. The first of these concerns the 

 shape of gregariues. The statement that gregarines are flat, like 

 treraatodes, is made in some text-books, but this is an error when 

 applied to the Polycystidea. The gregarines of this group are 

 monaxial animals, with a circular ci'oss-section, and any plane 

 passing through the axis divides them into morphologically identical 

 halves. This is shown by sectioned gregarines, and it may readily 

 be seen by watching the living animals. 



* Tlie date, 1900, given by Calkins to Siedlecki's paper is incorrect. 



