ECHINODERMATA. 
323 
throw it out by contraction, must also contribute to the process of re- 
spiration. There are found, namely, between the roots of every two 
tentacles, on a small papilla-shaped elevation, sometimes four, some- 
times five openings, from which canals pass in through the covering of 
the body to the cavity, giving entrance and exit to the water. With 
respect to the organs of propagation, Quatrefages has discovered the 
Synapta duverncea to be hermaphrodite. He could not discover any 
nervous system. 
Agassiz has turned his attention to the Echinidce, in his monographs 
above mentioned. 
The first livraison of this work embraces the genus Salenia (Mono- 
graphies Echinodermes, Ire livrais. contenant les Salenies. Neuchatel, 
1838), which, containing only fossil species, we shall not analize here. 
The second contains the Scutellce (1841.) Agassiz arranges these 
Echinodermata in that division of the Echinidce which he has called 
Clypeastroides, and which have, as a chief characteristic, a central 
mouth and a sub-central anal opening. Agassiz holds it unsuitable 
to unite the Scutellce into one genus as later Naturalists have done ; and 
he was constrained, as he took into consideration the internal organiza- 
tion, partly again to re-establish older genera, and partly to add new, 
by which means he makes thirteen genera, in which the position of the 
anal and sexual openiugs, the figure which the ambulacra form, the 
structure of the organs of mastication, and the cavity of the body, fur- 
nish the principal points for their characters. 
The shell of the Scutellce, like that of the Echinidce, is composed of 
ten regions of plates, of which five rows bear ambulacra, and the five 
without them lie between ; each region is formed, properly, of a double 
row of plates, which are so intimately united to each other, that they 
can hardly be separated. Round the mouth, instead of twenty plates, 
there are usually only ten or five to be counted, which form the buccal 
rosettes so called ; the spiniferous Scutellce rest upon the tubercles on 
which the spines are situated, as in Echinus. Of these tubercles the larger 
may be distinguished as spiniferous tubercles, and the smaller as miliary. 
The ambulacra, which form a five radiated rosette on the dorsum of 
the Scutellce, are as yet very little known. Agassiz was able to observe, 
on a very well preserved, although dried specimen of Laganum rostra- 
turn, that a row of lamellas was situated on the inner side of the ambu- 
lacral pores, which evidently stood in connection with them. From 
this it is to be concluded, that in the Scutellce the same organiza- 
tion of the ambulacra occurs as in the Echini, and that these lamellse 
indicate the dried branchial sacs. The Scutellce are very remark- 
ably and peculiarly distinguished by the ray-like furrows going out 
from the centre and ramifying on the under surface of the shell; in 
these furrows are also found a number of pores, which, like the pores of 
367 
