GREVILLE^ ON NEW DIATOMS. 231 



careful examination. The smooth and apparently structure- 

 less investing substance^ however, by the action of certain 

 reagents, is prone to separate into regular longitudinal fibrillse, 

 and these again into granules or sarcous elements. Such a 

 separation may be readily produced by a short maceration of 

 the muscles in a weak sokition of chromic acid. This change, 

 however, is very different from the irregular breaking up of 

 the fibre to which I have just alluded, and is in every respect 

 identical with the fibrillation and striation which takes place 

 at a little later period in the natural course of development. 



These fibres are rather larger in mammalia than in the 

 chick. They differ also from those of the latter in not being 

 so frequently constricted at short intervals between the 

 nuclei. The nuclei, moreover, are rather larger, and in 

 general disposed with greater regularity along the axis. 



In a foetal sheep of 3| inches in length, the fibres 

 were in nearly the same condition as those of the chick 

 on the fourteenth day of incubation. The central granu- 

 lar axis had entirely or almost entirely disappeared, for 

 the tubular substance which invested it now constituted 

 the whole or nearly the whole thickness of the fibre. Now, 

 also, it divided longitudinally into fibrillae, and these in 

 turn became resolved into granules or sarcous elements, 

 which were so small and close together that at first sight 

 the fibrillae appeared to be plain, and no indication of 

 transverse striae was perceived. Moreover, the nuclei had 

 enlarged, had become much more elongated in the direction 

 of the fibre and nearer the surface, but were still as perfect 

 as before. On the surface were a number of others, which were 

 smaller, and round or oval, and evidently engaged in con- 

 tributing new fibres by the process already described. As 

 the fibres advance in development the internal nuclei dis- 

 appear, and the sarcous elements and striae become larger 

 and more distinct. 



{To he continued.') 



Descriptions of New and K-are Diatoms. Series VII. 

 By R. K. Greville, LL.D., F.R.S.E., &c. 



Synedra. 

 Synedra Normaniana, n. sp., Grev. — Valve linear-club- 

 shaped, with side view unequally curved, attenuated towards 

 each obtuse extremity ; maximum of breadth at about one 



