18 TROCEEDINGS OF THE ACADEMY OF [Jan., 



gregarine with the cover-glass to be different in this region from 

 wliat it is in the more posterior parts. Further, since the transverse 

 movement takes place at the same time as the backward movement, 

 that part of the gregarine' s surface where the contact relations are 

 temporarily different moves not only backward, but from side to , 

 side as well. It is not difficult to see how movements of this sort 

 may produce locomotion, when it be recollected that gregarines 

 are sticky. If a particular part of the surface be in close con- 

 tact with the cover-glass or slide, a muscular movement which car- 

 ries this particular part backward would not be followed by a mere 

 slipping of this part, but by a movement of the gregarine in the 

 opposite direction. It is easy to see, when obserxing the upper sur- 

 face of a progressing gregarine, that the contact relations of differ- 

 ent parts are different. The upper surface loses its normal curved 

 contour, and shows considerable irregularities. The observational 

 conditions are too difficult to permit the changes of contour to be 

 followed, and in consequence wholly direct evidence that progression 

 is brought about in the manner outlined above is not to be had. It 

 seems to me, however, that the explanation of gregarine progression 

 here given is, on a priori grounds, more probable than that given 

 by Schewiakoff, for it is based on the fact that gregarines possess 

 a weU-developed muscular system, and it is in line with the general 

 principles of animal locomotion. 



On the other hand, a passive locomotion by means of the extru- 

 sion of gelatinous threads is without parallel in the animal kingdom. 

 Moreover, when the form of certain of the polycystid gregarines is 

 taken into account, this mode of progression is almost incon- 

 ceivable. Thus, Porospora gigantea, which inhabits the intestine of 

 the lobster, is shaped like a serpent, and is about forty times as long 

 as it is broad. Several genera, Dactylophorus, Schneider la and 

 Stichospora, for examples, have the form of greatly elongated 

 cones, with the posterior end terminating in a point. Specimens 

 of Echinomera hlsplda frequently show an outline which recalls 

 tliat of a tadpole. It is difficult to believe that the projection of 

 gelatinous fibres from the exti-eme posterior ends of animals of this 

 shape could push them forward. 



It may not be amiss to call attention to the conditions in other 

 Sporozoa. An adult coccidian possesses no muscular system, and 

 lacks the power to move. On the other hand, intra-cellular grega- 



