THE SPOROZOA 



181 



in many Flagellata, such as Euglena, for which reason these move- 

 ments were termed by Lankester " euglenoid." In the second 

 place, many Gregarines possess the power of gliding forward at a 

 great pace without any noticeable change of form, and without 

 any apparent mechanism for producing their rapid progression. 



The contractions and euglenoid movements of the Gregarine 

 body are sufficiently accounted for by the myocyte-fibrillae, if the 

 latter be assumed to be endowed with a power of contractility 



similar in its action to that of 

 ^f f ordinary muscle-fibrils. But the 



gliding movements of Gregarines 

 have always been a great puzzle. 



FIG. 26. 



Longitudinal section of a Gregarine 

 in the region of the septum between 

 protomerite and deutomerite, semi- 

 diagrammatic. Pr, protomerite ; De, 

 deutomerite ; s, septum ; en, endo- 

 plasm ; ac, sarcocyte ; c, cuticle ; m.f, 

 fibrils of the myocyte ; g, gelatinous 

 layer between sarcocyte and cuticle. 

 (After Schewiakoff, x 2000 diameters.) 



Fio. 27. 



Gregarlna munieri (A. Schn.), 

 (par. Timarcha tenebricosa), show- 

 ing the network of myocyte 

 fibrillae. (From Lankester.) 



The first satisfactory attempt at an explanation was given by 

 Schewiakoff [26], who accounted for the forward progression by 

 the extrusion of gelatinous fibres from the hinder end of the body. 

 The fibres in question are derived from a clear homogeneous layer 

 lying between the cuticle and the sarcocyte, and pass out 

 from the body through minute slit-like pores in the furrows be- 

 tween the ridges of the cuticle ; they then run backwards in the 

 furrow towards the posterior end of the body, becoming stiffened 

 by the action of the surrounding medium, and project free from 

 the hinder end of the animal. The numerous threads thus 

 produced form a hollow cylinder which by its continued growth 

 and elongation pushes the Gregarine forward. Schewiakoff's 

 explanation has met with general acceptance, but very recently it 

 has been criticised by Crawley [12]. This author confirms the 

 extrusion of a gelatinous substance, but denies that it is the cause 

 or agency of progression, or could possibly be so in many cases, 

 especially in the elongated serpent-like forms, such as Porospora 



