REMARKS ON THE STRUCTURE OF GREGARINiE. 343 



10 a Immersion) I have quite satisfied myself of the existence 

 of these hoop-like fibrillte and of the perfect accuracy of 

 Prof, van Beneden's drawings and description. But I can- 

 not look upon these fibrillae as muscular in the unreserved 

 manner in which their discoverer does. To quote his own 

 words applied by him to the protoplasmic cortical substance 

 to which I and others have previously ascribed the motor 

 powers of the Gregarinse, we may say, " Nothing, however, 

 proves the muscular nature of this coating; the transverse 

 (longitudinal) striations are not muscular transverse (longi- 

 tudinal) fibrils, but the result of a thickening, following a 

 transverse direction, of the cortical (or we may say of the 

 cuticular) substance." Professor van Beneden does not 

 adduce any evidence whatever of the contractility of these 

 circular fibrils, and it is difficult to see how he could. 

 Whilst of their existence there is not the least doubt, I do 

 not knoAV of any reason for regarding them as anything but 

 hoop-like ridges or thickenings of the cuticle, excepting this, 

 that they do not project from the outer surface, but are dis- 

 posed on the inner face of the cuticle. The cuticle is, as I 

 shall show directly, subject to various markings in the 

 Gregarinida as in Infusoria. In any case we have present 

 in G. yigantea the cortical protoplasmic substance, of the 

 contractility of which it is quite easy to satisfy oneself. 

 Such a Gregarina as Monocystis nereidis (fig. 2) leaves no 

 doubt in the mind that the cortical substance is the seat of 

 those changes of dimensions which give rise to the animal's 

 locomotion. The anterior region (m) in this species, and 

 also in Monocystis ascidice, presents an enlargement or ex- 

 pansion of the cortical substance (not to be in any way con- 

 founded with the anterior chamber of the bilocular Grega- 

 rina?), Avhich is eminently mobile, changing frequently its 

 relative length and breadth. 



This expansion exhibits a permanent delicate longitudinal 

 striation of its substance, not superficial, but deep and in- 

 dicative of fibrillation. There is no trace in these forms of 

 anything corresponding to Prof, van Beneden's muscular 

 coat. They seem to me, together with the fact observed by 

 me in many Gregarinse of the concomitant decrease in 

 motility and bulk of cortical substance, which is seen, as the 

 Gregarinse increase in size, and develope an abundant granu- 

 lar medullary substance, to warrant the view that the cortical 

 substance of the Gregarinida is the contractile substance. 

 Hence I should not like to pronounce the cortical substance 

 of this particular Gregarina from the lobster to have lost its 

 power (which, indeed, Prof, van Beneden does not altogether 



