53 



are living, active, and contractile, and I believe that, from this 

 point of view, one may say that the Gregarina gigantea is the 

 largest simple cell which is known. 



In our Gregarina a membrane with a double contour can be 

 very clearly distinguished, perfectly transparent, and without 

 structure. It presents no opening, and its thickness is 

 throughout the same, excepting, howevei', at the anterior 

 part of the rounded bulb which terminates the body of the 

 animal in front. This structureless membrane represents the 

 " cell membrane " of this monocellular animal. 



Under this membrane can be distinguished clearly a layer 

 of some resistance, formed of a substance which is perfectly 

 transparent and devoid of granulations. It is this structure 

 which Leidy and Ray Lankester first made known, and I 

 have been able fully to establish in this species that it is truly 

 in this layer that the parallel strise arise, whence results that 

 fibrillar aspect of the animal which one remarks on using 

 high powers. It is when the Gregarina contracts that these 

 striae appear, and they disappear when it is in repose. I 

 believe, Avith Leidy and Eay Lankester, that the substance 

 which constitutes this layer possesses essentially contractility, 

 and that it is this which is concerned in the production of the 

 movements of which the animal is capable. It represents, 

 physiologically, the muscular subcutaneous layer of many 

 animals more elevated in organisation, and of Nematodes 

 especially ; but instead of being formed of distinct muscular 

 fibres it is a continuous layer of contractile, — if you like, 

 muscular — substance. 



The consistence of this layer is much greater than that of 

 the granular matter which occupies the centre of the cellular 

 tube. The central granular matter is very mobile ; it moves 

 about in the interior of the cavity of the cell. This is by no 

 means the case with the transparent and contractile substance 

 of which we were speaking; this is fixed and intimately 

 blended with the membrane of the cell. The limits between 

 this layer and the granular matter of the centre are, however, 

 not sharply marked. I imagine that the density of the layer 

 decreases from the periphery towards the central axis of the 

 tube. 



The thickness of this layer is nearly the same throughout 

 the whole length of the animal. It augments, however, a 

 little at its anterior extremity, principally at the point of 

 union of the globular enlargement with the rest of the body. 

 There, this layer sends a prolongation inwards in the fonn of 

 a transverse septum to the interior of the tube, in such a way 

 as to divide the central granular mass into two parts, of 



