8 Maurice Croivthcr Hall 



the longitudinal cuticular ribbing and also to the folding of the 

 ectosarc. Van Beneden (1872) regarded Leidy's longitudinal 

 striation as accidental, and adopted the view of Lankester and 

 Leuckart, that the striae originate in a folding of the cortical layer. 



Observations on the gregarine from Mclanoplns indicate that 

 the longitudinal striation is due primarily to the cuticular ribbing, 

 but does not correspond to it to the extent that the number of 

 striae visible is identical with the number of ribbings on the sur- 

 face under observation. The distance between the cuticular 

 lamellae is fairly constant and very slight, about 0.5 /x. On the 

 other hand, the distance between the visible striae is very variable 

 and much in excess of the figures given for that between lamellae, 

 ranging from 2 /x to 10 |U,. Magalhaes (1900) similarly records 

 those of Grcgariiia bhtfariim as 7 fj. apart. Moreover, the lamel- 

 lae are continuous from end to end of the animal, whereas the 

 striae are quite uniformly shorter than this and usually lap ends 

 in the region of the septum. The striation wdiich is due to the 

 true cuticular lamellae arises from light rays striking these ridges 

 at such an angle as to be refracted to the ocular where they be- 

 come visible. In a young gregarine from Eritcttix I have found 

 that changing the position of the eyes would shift the striae from 

 side to side. In dealing with a curved surface, such as the gre- 

 garine body, it would naturally be expected that the light refrac- 

 tion would be visible at intervals varying in dififerent individuals 

 and in different parts of the same individual, and that even these 

 light areas would probably become discontinuous at intervals and 

 especially at the ends of the body and in the neighborhood of the 

 septum where a new factor of curvature is introduced. 



Aside from the above, other factors enter in from the folding 

 of the cuticle or the entire ectosarc, such as is shown in cross- 

 section ( fig. I ) and in the view of a specimen treated in toto wath 

 gold chloride (fig. 21). Such foldings complicate the light re- 

 fraction of the cuticular lamellae and also add ne\v' striations to 

 which the cuticular lamellae liave a minimum of causal relation. 

 It would naturally be expected that folding in a longitudinal plane 

 would occur in a surface in which a set of relatively stiff longi- 

 tudinal ribs already existed to give direction to the folding. 



156 



