1905.] NATURAL SCIENCES OF PHILADELPHIA. 97 



merit of the entire animal in an opiDOsitc direction. The movement 

 will be rectilinear or zigzag, dependent on the less or greater extent 

 of the transverse movement. This last, in its turn, depends on the 

 extent of the oscillation of the protomcrite. Hence, when the grega- 

 rine is advancing in a straight line, the evidence for muscular action 

 is very slight. 



My observations also indicated that gregarines arc sticky, and that 

 they do not seem able to progress unless in contact with a surface. 

 I was therefore led to postulate the stickiness as more or less of a neces- 

 sity in progression, its role being to prevent slipping of the particular 

 part in contact with either the slide or cover-glass. Later observatioixs, 

 however, have led me to modify this opinion. Contact appears neces- 

 sary, but not necessarily contact with a continuous surface. The 

 observations were as follows: 



The host intestine was teazed on a cover-glass, under a limited 

 quantity of salt solution. The cover-glass was then inverted, and 

 supported on a ring. In this way a mount having considerable depth 

 was obtained. The results were to show that gregarines are able to 

 progress away from a surface provided they can get into contact with 

 some solid matter. One, originally moving on the surface film on the 

 bottom of the drop, pushed its way upward through the particles of 

 host intestine. In such cases, however, progression is slow and ap- 

 parently difficult, and accompanied by constant and violent contortions. 

 It may, moreover, be stated that in proportion as the environment 

 renders progression more difficult, the evidences for muscular activity 

 become more obvious. Thus, when an advancing gregarine encounters 

 a mass of loose host tissue, it frequently endeavors to bore or wriggle its 

 way through, and muscular contractions at once become very exten- 

 sive. 



The abihty of gregarines to make their way amidst particles of solid 

 in a hanging drop suggests that, in some cases at least, progression is 

 effected in somewhat the same way as that of a snail. The presence 

 of an adhesive substance on the surface may assist, but the primary 

 factor is the alterations of the contour of the surface. These are doubt- 

 less by no means so regular as those of the foot of a snail, nor is gre- 

 garine progression usually so smooth. Yet, without going into tedious 

 details, it is easy enough to see how such movements could produce 

 progression. When, however, progression is being effected on a smooth 

 surface, the adhesive substance probably plays a part. 



A curious phenomenon was once exhibited by a little gregarine of 

 Scolopocryptops sexspinosus. This is a very active species, progressing 

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