314 E. RAY LANKESTER. 



do), and to have transferred it to the layer of circular fibrils, 

 the contractility of Avhich is altogether hypothetical. More- 

 over, I cannot suppose that this layer of circular fibrils exists 

 universally in the Gregarinida. Certainly nothing so obvious 

 as are these fibrils in the lobster's Gregarina can have 

 escaped detection in the well-studied Monocystis lumbrici, in 

 M.nereidis (studied by me with a y^th Powell and Lealand), 

 nor in the M. sijiunculi to be described below. It is necessary 

 without doubt to re-examine the structure of other Gregarinaj 

 in the light of Prof, van Beneden's observations on G. gigan- 

 tea, and those who have the opportunity will, it is to be hoped, 

 shortly make known the results of renewed observations. 



If those who would advocate the muscular nature of 

 Van Beneden's layer of transverse fibrils will admit that 

 this layer is not differentiated in some species of Grega- 

 rinida, I think we obtain some argument against its mus- 

 cular character ; for G. gigantea is not a AvonderfuUy active 

 organism, as -would be expected from such an extensively 

 developed muscular coat. It does not exhibit movements 

 which differ in kind from tbose of the Gregarinse, which 

 depend simply on the but slightly differentiated protoplasm 

 of their cortical layer, that is to say, it does not exhibit 

 movements which can be called muscular (distinguished by 

 their definite recurrence and rapidity), in distinction from 

 such as may be called protoplasmic. Though it is not 

 possible to draw a sharp line between these two kinds of 

 movement, nor between the two structural conditions with 

 which they are associated, yet the very advanced condition 

 of differentiation w^hich the fibrils of G. gigantea would 

 indicate, if regarded as muscular, justify the expectation of 

 some marked contrast between its movements and those of 

 such a form as M. nereidis. The fact appears to be that M. 

 nereidis is the more active of the two. It certainly exhibits 

 far greater activity in changing its shape than G. gigantea, 

 which, as far as I have observed, never exhibits a change of 

 dimensions, but glides along in that rather mysterious man- 

 ner which is also seen in G. blattarwn and M. sipimculi, and 

 which, from what I saw in a gigantic specimen of the latter 

 species, one eighth of an inch long, appears to be due to a 

 slight but continuous undulation of the lateral margins of 

 the body. The Gregarina has in this case, and in all pro- 

 bability generally, not a truly cylindrical, but a flattened 

 fluke-like shape. With regard, then, to Van Beneden's 

 muscular layer of circular fibrils, I w^ould conclude that its 

 muscular nature is purely hypothetical, that it is not to be 

 looked upon as an essential part of the organisation of the 



