S LADEN ! STRUCTURE OF ASTEROIDEA. 
281 
am not aware that that naturalist has availed himself of the deduc- 
tions which necessarily follow. When describing the Starfish it 
may be remembered that I drew attention to the presence of a 
peculiar madreporiform body, situated between the margin and the 
centre, on the upper or dorsal surface of the disk, and which formed 
the orifice of the water- vascular system. In the Ophiuroidea the 
position is altogether different, the orifice being found on the ventral 
or under surface and occupying one of the plates that surround the 
mouth. Now in this very striking difference there lies — although 
it may seem strange at first thought — a highly important point of 
evidence in support of the argument which this paper maintains. 
In an early stage of the development of an Asteroid, shortly 
after the young starfish larva has emerged from its brachiolaria 
phase, the plate that bears the punctures of the water- vascular 
system, and which eventually becomes the madreporite, is situated 
on the under side, and close adjoining the plates that form the 
margin of the mouth. In other words, we have again presented to 
us in the larval Asteroid, the precise arrangement of parts that 
occurs in the Ophiuroidea when in the mature form ; and from 
this we are led to infer from our present knowledge of the laws of 
embryology, that the Asteroidea have in the course of the history of 
their race, passed through a stage which is now represented — in a 
more or less modified style, it may be — by the present Ophiuroidea, 
Notwithstanding the existence of these resemblances in struc- 
ture, it has always been held that the Asteroidea and Ophiuroidea 
were separated by a wide gulf of difference, over which no known 
echinoderm presented sufficiently modified characters to form a 
bridge, and which w^ould serve as an index of their closer ancestral 
alliance. Recently, however, there has been discovered a remarkable 
organism of most abnormal form, undoubtedly intermediate be- 
tween the two groups, and which passes unquestionably very much 
further over the borderland that lies between them than auy other 
star fish or brittle-star with which we have hitherto been acquainted. 
Space will not permit me to enter further into the description 
of this curious organism, than to say that it appears to present the 
