31 



liche Kieseihiille gebildet, in oder iinter welcher die Fuss- 

 plattchen der Stacheln festsitzen." It does not appear that 

 they can ti'uly be hekl imbedded in a rigid pellucid siliceous 

 coat, from the strong reasons previously adduced. The inter- 

 vening bond of union^ whatever it may be, has then no con- 

 nection with the central sarcode body, for the spines can 

 independently maintain their mutual position, and yet this with 

 greater or less readiness gives way to forces sometimes from 

 within, and most likely sometimes from without, and in the 

 living animal recovering position and coherence, as, for in- 

 stance, pressing on the covering glass, or the action of the 

 little parasitic rotatorian previously described by me. In 

 addition to the fact of finger-like protrusions of colourless 

 sarcode being projected and withdrawn, one sometimes sees 

 likewise two individuals of A. turfacea united by an isthmus 

 (" conjugated" ?) (shoAving that the spines can recede from one 

 another and come back to position) the isthmus gradually 

 stretched, till it becomes a mere connecting thread of sarcode, 

 which eventually snaps, and the two examples pass aM^ay from 

 one another, no trace of the place from which the mutual 

 band of sarcode emanated being left. Can such examples 

 represent the state of " fission" (Zweitheilung), adverted to 

 by Greef, as one of the reproductive conditions of A. tur- 

 facea ? Under ordinary circumstances, the circular discoid 

 bases of the spines must leave triangular spaces between, 

 quite large enough to allow of the jjassage forth of the or- 

 dinary pseud opodia through the medium which we must 

 assume causes the mutual coherence of the spines, and this 

 without any displacement of the latter. 



In this genus Acanthocy^stis Greef brings to notice three 

 other forms ; two he names as new, and the other he leaves in 

 abeyance. One, which he calls Acatithocystis pallida, seems to 

 me to diiter in no respect from A. turfacea further than in the 

 absence of the green colouring granules, except that he attri- 

 butes to it the existence of the bacillar or linear spicula said to 

 occur along with the radial spines, and as to which, indeed, he 

 is silent as regards Carter's form. But, as I have mentioned, 

 I now am quite disposed to hold these as very problematical. 

 There remain only then the colourless granules to distinguish 

 this form from A. turfacea. Now, quite colourless examples of 

 what I have always thought could be none else than A. tur- 

 facea often occur here ; nay, examples present themselves 

 with a great proportion of the body mass bearing the green 

 (chlorophyll) granules, and the remainder colourless, and 

 these regions marked by a sudden transition. I think the 

 same green granules sometimes become colourless. We see 



