STUDIES IN THE EMBEYOLOGY OP ECHINODEEMS. 437 
grounds ( 15 , p. 79), that the madreporic plates of Asterids and 
Ophiurids are homologous, would receive new and striking 
support. 
Agassiz ( 2 ) and Gotte ( 11 , p. 620) both describe the basals 
of Asterids as formed round the right enterocoel, but as the 
value of their testimony is in some degree weakened by their 
mistake with regard to the terminals, it will be well to give 
some further evidence ; without, therefore, referring to the 
numerous arguments to which Ludwig’s suggestion has given 
rise, I shall give the result of my own observations on Bipin- 
naria and Asterina. In the former most of the basals are 
formed late, and I have not obtained specimens which show 
their position satisfactorily. At first sight the case above 
mentioned, in which the madreporite and terminals are all in 
the same straight line, seems to indicate that the former also 
belongs to the left side ; but on cutting sections we find that 
it does not lie over the enterocoel, but over another cavity 
which has not been noticed by previous observers ; this cavity 
is situated in the median line, and is utterly unconnected with 
the enterocoel in any stage in which I have observed it ; and 
though I have not with certainty traced its formation, I 
believe it to be of schizocoel origin, like the similarly situated 
“ pulsating vesicle ” in Echinids ; it is, however, not contrac- 
tile, but contains a few corpuscles which are kept in move- 
ment by cilia on the walls of the sac ; it is most probably the 
rudiment of the blood-vascular system, but I cannot at present 
assert this positively. 
Since nothing could be determined as to the position of the 
basals from such a larva as this, I next turned my attention to 
Asterina gibbosa, in which, as Ludwig had already made 
known, all five basals (including the madreporite) appear at an 
early period. Here, however, I met with an unexpected diffi- 
culty, for it was soon evident that my larvae (obtained at 
Naples in May, 1888) did not at all agree in their internal 
anatomy with Ludwig’s description. I must therefore, for the 
present, ignore his account (accepting only such parts as relate 
to the external form, and to the position and nomenclature of 
