98 PROCEEDINGS OF THE ACADEMY OF [Jan., 



continually in straight lines and curves of long radius. It would occa- 

 sionally give a sudden jerk, and advance by perhaps its own length by 

 a leap. This ability to leap was never seen in any other species. 



There finally remains for consideration what is probably a form of 

 the progressive movement. Prior to cucystment gregarincs pair, the 

 association in a genus like Gregarina being apparently only precocious 

 pairing. It may be "head to tail" as in Gregarina, or "head to head" 

 as in Pterocephalus. In either case the pair bends double at its middle 

 point, thus 1:)ringing the gregarines side by side. Before or during this 

 last, process the system begins to rotate. During the course of this 

 rotation the two individuals become more and more closely apposed 

 until a spherical form is assumed. Meanwhile a common covering 

 is secreted, the cyst formed and eventually the rotatory movement 

 ceases. 



This movement is generally mentioned by those authors who have 

 made observations on the encystment of gregarines, but no attempt ap- 

 pears to have been made to account for it. Biitschli (1881), however, 

 states that muscular contractions are to be observed at the time when 

 the two animals begin to fuse. The explanation advanced by Schewia- 

 koff, that gregarines progress by means of the extension of a stalk of 

 gelatinous fibres, is here manifestly inapplicable. Further, since 

 according to the accounts the rotation continues until after a certain 

 amount of a gelatinous investment is secreted, changes of surface con- 

 tour would not seem to be of effect. One point, however, is worthy 

 of attention. The rotation, both in nature and when the gregarines 

 arc on the slide, doubtless takes place when the animals are suspended 

 in a liquid. The only opposition which the rotation encounters is 

 then the friction of this liquid, and this would be almost infinitesimal. 

 That is, it does not seem necessary to assume that the impulse lasts 

 as long as the rotation itself. The latter, once started, would continue 

 of its own momentum for probably a considerable period of time. 



Accurate observations are, nevertheless, a desideratum, and, as I 

 have stated, these are yet to be made. I have, however, at times 

 observed a rotation on the part of solitary gregarines. One case was 

 particularly striking. The gregarines, specimens of Trichorhynchus 

 pulcher Aime Schn., holding the body bent, moved around the circum- 

 ference of a circle. The curved longitudinal axis of the animals formed 

 an arc of this circumference, the radius of which was perhaps one-half 

 the animal's length. That part of the circumference not occupied by 

 the gregarine was filled with a mass of sundry small particles, the 

 movements of which followed that of the gregarine. That is, there 



