1902.] NATURAL SCIENCES OF PHILADELPHIA. 19 



rines, wheu squeezed out of the cell?, show muscular coutortious, 

 and occasionally the typical progression of the free-living sporont. 

 The Hsemosporidia and IMyxosporidia, both of Avhich are motile, 

 possess muscle fibres similar to those of polycystid gregarines, 

 whereas the Amoebosporidia (Schizo-gregarines) show no muscle, 

 and are not known to possess the power to move. In general, 

 throughout the Sporozoa, the possession of muscle fibres and the 

 power of moving from place to place go hand in hand, while the 

 forms which are not knoAvn to move lack muscular elements. It 

 would, therefore, seem somewhat extraordinary if the polycystid 

 gregarines, in which the musciUar system is well organized, should 

 have developed such a unique mode of progression as that described 

 by Schewiakoff. 



Bibliography. 



Calkins, G. K, 1901. Columbia University Biological Scries, No. 6» 



Tlie Protozoa. New York, The Macmillan Co., 1901. 

 Delage et Herouard, 1896. Traite de Zoologie Concrete, Tome I, La 



Cellule et les Protozoaires. Paris, Schleicher Freres, 1896. 

 Doflein, F., 1896. Die Protozoen als Parasiten und Krankheitserreger. 



Jena, G. Fischer, 1896. 

 Frenzel, J., 1891. Ueber einige argentinische Gregarineu. Ein Bei- 



trag zur Organisation und Physiologic der Gregarinen iiberhaupt. 



Jena Zeitschr., Bd. 27, pp. 233-336, Taf. 8. 

 Labbe, a., 1899. Das Tierreich ; 5 Lief., Sporozoa. Berlin, R. Fried- 

 lander und SohD, 1899. 

 Lang, A., 1901. Lehrbuch der vergl. Anatomic der wirbelloseu Thiere. 



2 Aufl., 2 Lief., Protozoa. Jena, G. Fischer, 1901. 

 Lankester, E. Ray, 1872. Remarks on the Structure of the Gregar- 



inae, and on the Development of G. (Mouocystis) sipunculi Koll. 



Quart. Jour. Micr. Sci.. N. S., Vol. 12, pp. 34>-3il, PL 20. 

 ScHAUDiNN, Fe., 1900. Untersuchungen iiber den Generationswechsel 



bei Coccidien. Zool. Jahrb., Bd. 13, Abth. f. Anat., pp. 197-292, 



Taf. 13-16. 

 Schewiakoff, V., 1894. Ueber die Ursachc der fortschreitenden 



BeweguDg der Gregarinen. Zeitschr. f. wiss. iZool., Bd. 58, pp. 



340-854, Taf. 20 u. 21. 

 Siedlecki, M., 1900. Ueber die geschlechtliche Vermehrung'der Mon- 



ocystis ascidiiB R. Lank. Bull, intern, de I'Acad. cles Sci. de 



Cracovie. Compt. Rendus des Seances de I'Ann. 1890, pp. 515- 



537, 1 pi. (Plate appeared in the number for May, 1901.) 



EXPLANATION OF PLATES I AND XL 



Plate I. — Fig. 1. — The successive positions occupied by a gregarine 

 {Slenophora juli) progressing in a zigzag. The line to the right shows 

 the nature of the path followed. 



Fig. 2. — The successive positions taken by a progressing gregarine 

 (StenophorajuU) wheu turning without alterations in the shape of the 

 body. 



