Mr. T. H. Huxley on the genus Thalassicolla. 435 



rounded apertures, so as to have a fenestrated appearance (fig. 6). 

 There were no spicula ill this kind. 



In a single specimen I found a similar shell, but its apertures 

 were prolonged into short tubules (fig. 5). 



Frequently the connecting substance in which the cells were 

 imbedded appeared to be quite structureless, but in some speci- 

 mens delicate, branching, minutely granular fibrils were to be 

 seen radiating from each cell into the connecting substance 

 (fig. 2 J). 



I have mentioned certain minute bright yellow spherical cells 

 contained within the shell of the fenestrated kind ; such coloured 

 cells are contained in all kinds either diffused through the con- 

 necting substance or more or less concentrated round each large 

 cell (figs. 3 a, 2 b). 



Th. nucleata. (PI. XVI. fig. 4.) 



This form consists of a spherical mass of jelly as large as the 

 middle-sized specimens of the last variety, with an irregular 

 blackish central mass. Enveloping this and forming a zone 

 about half the diameter of the sphere there is a number of clear 

 spaces — vacuolse — varying in size from -g^nd- to arW^h °f an 

 inch, the smallest being innermost. Scattered among the vacuolse 

 of the innermost layer, there were many of the yellow cells, 

 and a multitude of very small dark granules. Delicate, flat- 

 tened, branching fibrils radiated from the innermost layer, pass- 

 ing between the vacuolar, and in one specimen these fibrils were 

 thickly beset with excessively minute dark granules, like ele- 

 mentary molecules, which were in active motion, as if circulating 

 along the fibrils, but without any definite direction. In this case 

 the whole body looked like a moss agate, so distinct were the ra- 

 diating fibrils (4 a) . Left to itself for less than an hour, however, 

 this appearance as well as the circulation of granules vanished, 

 and only a few scattered radiating fibrils were to be observed, the 

 rest seeming to have broken off and become retracted. 



By rolling under the compressor the outer mass could be 

 completely separated from the central dark body, which then ap- 

 peared as a spherical vesicle ^jtii of an inch in diameter (fig. 4 b), 

 showing obscurely a granular included substance, 



The membrane of the vesicle was very strong, resisting and 

 elastic. When burst it wrinkled up into sharp folds (fig. 4 c), 

 and gave exit to its contents (fig. 4d). These were — 



1. A very pale delicate vesicle (nucleus?) without any con- 

 tents, and measuring (but when much compressed) about ^th 

 of an inch (fig. 4 d). 



2. A heterogeneous mass consisting of (a) a finely granular 

 base, (b) oil-globules of all sizes, (c) peculiar cells F ^th to y^Vntk 



28* 



