1905.] NATURAL SCIENCES OF PHILADELPHIA. 91 



great differences exist in the first of these in different gregarincs. I 

 shall now consider the contractile element. 



This is evidently the myocyte. The evidence that the myocyte is 

 contractile is purely inferential, but none the less satisfactory. The 

 fibre is the form always taken by differentiated contractile substance. 

 Other protozoa, ciliates and flagellates, show like elements, and most 

 of the movements displayed by polycystid grcgarines are compre- 

 hensible only by assuming the myocyte to be a contractile system. 

 On the other hand, certain movements exhibited by the polymorphic 

 species cannot so readily be explained in this way, as I shall presently 

 show. 



Confining our attention for the moment to these movements for 

 which the myocyte seems an adequate cause, they are found to be dis- 

 played by all gregarines. They are, however, as we should expect, 

 far more definite in the elastic than in the polymorphic species. The 

 most usual are mere bendings of the longitudinal axis, the character 

 and extent of which appear to depend largely upon the shape of the 

 gregarine and the nature of its eclosarc. The least extensive are 

 bendings of the protomerite, which may take place in any plane. 

 These may be so slight as to be difficult to detect, or so extensive that 

 the axis of the protomerite comes to form a right angle with that of 

 the deutomerite. They readily lead to a distortion wherein the angle 

 in the longitudinal axis is formed in the deutomerite instead of at the 

 septum. This may be a right angle even in such relatively thick 

 species as Stenophora julipusilli Leidy. In Gregarina dicceli Crawley, 

 which is a vermiform gregarine with a thin epicyte and no sarcocyte, 

 this distortion becomes more evident. The protomerite and anterior 

 part of the deutomerite bend round to form a hook, the anterior surface 

 of the protomerite being directed backward. As the point in the longi- 

 tudinal axis where the original bending takes place moves further and 

 further backward, the hook becomes larger and larger until the gre- 

 garine forms a U. This U may pass into a circle and the circle into a 

 coil or a spiral. Gregarina polydesmivirginiensis Leidy^ displays con- 

 tortions of exactly the same character. Animals such as S. julipusilli 

 Leidy frequently bend double, but the circular or coiled condition can- 

 not well be assimied by any but the long slender gregarines. 



When only the protomerite is involved, the movement is frequently 

 first to one side and then to the other. This may also happen when the 

 anterior part of the deutomerite participates along with the proto- 



^ According to L^ger et Duboscq (1903), this species belongs to the genus 

 Stenophora, since it stands very close to the Stenophora nematoidesoi these authors. 



