328 
HERBERT P. CARPENTER 
admits that it is not ; and the mere fact that in some Urchins 
and Starfishes the genital ducts do not open on the genital 
plates does not seem to me a sufficient argument to meet 
this difficulty, though, according to hini, Indessen stort 
das die Homologie, die nach Obigem zweifellos zwischen den 
Mundschildern der Ophiuren und den Genitalplatten der 
EcUnoideen und Asterien hesteht durchaus niclit ”(!!!) 
Ludwig nowhere says a word about the genital plates of 
the Ophiurids, and yet these are developed interradially on 
the abactinal surface of the larva precisely like the genital 
plates of the Starfishes. The following passage from 
Agassiz Q North American Starfishes,’ p. 98) is interesting 
as regards this question : 
“ In Opliiurans the genital plates are formed from the angles of the five 
interradial plates ; similar plates can still be traced in the young Starfishes, 
while in the full-grown Starfishes their presence is shown by the interbra- 
chial partition, on each side of which the ovaries discharge. Thus there 
exists a complete homology between the genital plates of Opliiurans and 
the interbrachial partitions of Starfishes, a homology fully carried out in its 
details when we examine the relations held by the genital plates to the 
ovaries in Ophiurans and by the interbrachial partitions to the ovarian 
openings in Starfishes.” 
Of course there are aberrant forms with more or less 
exceptional peculiarities among the members of each class, 
but the general relations of both classes are such as entirely 
to support the statements quoted above, while the peculiar 
features of the exceptions [Asterina gihhosa, Trichaster 
elegans^ &c., as shown by Ludwig’s own observations) seem 
to me to be of such a nature that they support Agassiz’s 
view rather than Ludwig’s very revolutionary one. 
The relations of the primary actinal and abactinal plates 
to the blood-vascular system may be looked at from another 
point of view than the one used hy Ludwig. A person 
standing in the central plexus (heart) of a young Starfish, 
with his feet in the oral blood-vascular ring, would have the 
genital plates above his head. But if he were similarly 
placed in a Crinoid (with the ventral side downwards) he 
would have the basals over his head, and not the orals, 
although these last are the homologues of the genitals of the 
Starfish according to Ludwig’s theory. 
Ludwig does not attempt to follow out to any great extent 
the logical results of his theory with respect to the relations 
of the various regions of the body among the different Echi- 
iioderms. But he points out (p. 819) that they involve our 
believing in a great difference between Urchins and 
