PROFESSOR W WELLE THOMSON ON THE ECHINUOERMATA. 409 
afterwards it becomes connected with, and part of, the ambulacral 
circulating system. When the ambulacral vessels and suckers of the 
young starfish become fully developed, this provisional vascular tuft 
withers and disappears, leaving no apparent scar. 
28. It is impossible to avoid at once recognizing in the vascular 
pseudembryonic appendage of Asteracanthion violaceus , the three 
water-feet of Brachiolaria. (§ 21.) Even the oval granular mass, 
whose significance is yet unknown, is in the same position in both. 
This pseudembryo of Asteracanthion exactly corresponds with 
Brachiolaria except in one point. The anterior third is attached 
immediately to the posterior third, while the central part, which in 
Brachiolaria bears the pseudostome and the swimming appendages, is 
undeveloped. A special assimilative apparatus seems to be unne¬ 
cessary. The young are crowded round the mouth of the parent, 
imbedded in a slimy mass of half digested food, to portions of which 
they are generally attached, at first by their peduncles and afterwards 
by their water-feet. Swimming appendages are of course equally 
unnecessary. In all this group of embryo the sarcode layer is by 
no means so transparent as in the swimming forms. It is loaded 
with very minute oil globules, and has the dulled transparency of 
ground glass, resembling the material of the young of some internal 
parasites. 
29. Prof. Sars # describes the embryogeny of Echinaster sanguino- 
lentus, O. E. Muller (— Echinaster sepositus , Petz. ; E. oculatus , 
M. & T.; and Gribella oculata , Eorbes.) This species produces its 
young in a marsupium, in the manner already described in Aster¬ 
acanthion violaceus . The pseudembryonic appendages had nearly the 
same form as in the latter species, but Prof. Sars describes them as 
at first placed towards the ventral aspect of the disk of the starfish, 
and afterwards passing over towards the dorsal surface, and, finally, 
disappearing in the position of the madreporic tubercle. He imagines 
the madreporic tubercle in starfish to represent the scar of the 
former attachment of the pseudembryonic peduncle, and he regards 
this peduncle as the equivalent of the stalk in Crinoids. I think 
there can be little doubt that this view of Prof. Sars, with reference 
to the madreporic tubercle, is a fallacy. The pseudembryonic vascular 
appendage represents the internal ciliated sac of Bipinnaria , and not 
the dorsal pore and tube, and from Muller’s observations on the 
Trieste Bipinnaria , the ciliated sac seems to be connected with the 
ambulacral ring, independently of the dorsal tube, though in close 
connection with it. 
However, as the sand-canal is essentially a portion of the am¬ 
bulacral system of the starfish, and in direct communication with 
that system, it seems by no means improbable that in those forms, 
such as Bipinnaria asterigera , in which the dorsal surface of the star- 
* Wiegmann’s Archiv. Part 2, 1844 ; and “ Fauna littoralis Norvegiae.”— 
Christiania, 1846. 
