522 
like body. Contrary to the opinion of Agassiz, the author regards 
these chords as truly representing a nervous system. 
The author described four spherical tubercles, situated two upon 
each side of the cushion-like body, and between it and the ten- 
ticular discs. These are the equivalents of exactly similar tubercles 
described by Agassiz in Cydippe, but not noticed by him in his 
description of Idyia. 
Development. 
In his account of the development of Beroe : the author described 
the ovum, after its escape from the surrounding water, as consisting 
of a spherical vitellus, surrounded by an external transparent and 
structureless shell, which is separated by a wide interval from the 
vitellus, the whole being at this time generally surrounded by an 
atmosphere of spermatozoa, which are in the form of very minute 
caudate corpuscles. 
No trace of germinal vesicle or spot could be detected in the 
vitellus, which has the appearance of being composed of minute 
cells, and whose peripheral portion is differentiated as a somewhat 
denser layer. A few hours after the escape of the ovum segmenta- 
tion begins, and this process goes on until the vitellus is broken up 
into numerous very distinct and quite free spherules, each of which 
is plainly a cell filled with a multitude of similar cells. The seg- 
menting process, however, has not been going on uniformly in all the 
divisions, and these resulting spherules are consequently of unequal 
size, and represent different stages in the process. Next, successive 
segmentations go on with great activity in some of the spherules, 
while others continue unaffected by it, or present it with much less 
energy, and the former become broken up into a multitude of cells, 
by which the latter are gradually enveloped ; so that the ovum now 
presents two very distinct portions — a central one composed of large 
spherical cells, and a peripheral one of much smaller cells. 
Simultaneously with the completion of the peripheral layer, a 
large lacuna is formed among the cells in the centre of the ovum. A 
depression — the future mouth— next takes place upon the surface of 
the embryo ; and this becomes deeper and deeper, until it reaches the 
central lacuna, into which it finally opens. At the same time, the 
ocelliform body, with its capsule, and the rudiments of the tentacular 
discs, become apparent. The refractile corpuscles of which the ocelli- 
