The Pluteus of Laganum sp. 141 
unlike that described for other related forms. Goto (2), in discussing | 
Asterias pallida, has maintained that ‘‘the plane of bilateral symmetry 
of the adult coincides with that of the larva, and that the oral side 
of the former is the anterior side of the latter and the aboral side the 
posterior.” This is almost the case in Laganum, where the anlage of 
the mouth of the adult is located in the anterior part of the ventral 
surface of the larva. In Asterias pallida this condition comes about by 
a gradual growth of the organs of the left side towards the median line. 
If the amniotic cavity of Laganum is formed in this manner it must be 
accomplished at an exceedingly early period, since in the specimens 
under observation no trace of any such previous condition remains. 
Moreover, if the formation of the amniotic cavity has been accom- 
plished by a separate invagination from the left side, the subsequent 
opening of the mouth into it presents an additional vexatious question. 
THE ENTEROCGELES. 
The median position of the hydroccele is also in striking contrast with 
the location of the corresponding structure in other echinoderms, in all 
of which it is described as lying on the left side. Since in this stage of 
Laganum all connection of the hydroccele with the anterior enteroccele 
has been lost and no direct evidence remains as to its mode of develop- 
ment, it seems unwarranted to ascribe to it an origin differing from that 
of other known forms. The structures that I have called the posterior 
enteroccele are still more unusual, not only on account of their different 
position, but also because of their striking dissimilarity in form from 
those of other plutei. They lie as two entirely separate spherical 
vesicles, ventral to the stomach on either side of the posterior lobe of the 
hydrocele. That they have had a common origin seems highly prob- 
able from their close resemblance to each other as well as from the fact 
that they stand in similar relation to the spines on the oral surface of 
the embryo. In many instances these spines, passing directly through 
the wall intervening between the embryo and the amniotic cavity, he 
with their tissues in direct contact with the lumen of the vesicles. The 
same condition occurs in forms where one of the vesicles has divided, 
and from the smaller anterior one other spines seem to emerge. 
That no structures are present corresponding to the right hydroccele 
and right posterior enterccele is rather remarkable considering the 
advanced stage of development of those of the opposite side. The 
undivided condition of the anterior enteroccele is less unusual, though 
not of common occurrence in other closely related forms. According to 
Bury (1), Echinoids and Ophiuroids possess two separate enterocceles 
which lie at the sides of the esophagus. Moreover, among the Asteroids 
the same condition obtains in the Bipinnaria. However, in the older 
stages of these forms a secondary fusing often occurs, especially in the 
region of the preoral lobe, so that a common cavity comes to be present. 
