194 WILSON. [Vot. II. 
birth, motionless on the surface of the water. They then ac- 
quired cilia, and began to swim feebly about at the surface, often 
collecting in rows at the sides of the vessel or in groups away 
from the sides. Lucaze Duthiers noticed the same habit in 
Astroides. At the end of a week the larvz are rapid swimmers, 
now spending most of their time below the surface of the water. 
Often they creep along the bottom and sides of the dish like 
little worms. Though they are constantly lengthening or 
shortening their bodies, the general shape is that of a pear, 
with the mouth at the small end. The broad end is usually, 
though not invariably, directed forwards in swimming. While 
creeping over the glass they frequently fasten themselves by 
their broad ends for from one to ten minutes, becoming free again 
of theirown accord. The larve continued to swim about without 
any change in form until the middle of April. By this time, as 
subsequent examination showed, they had acquired six mesenter- 
ies (three pairs) and two long mesentrial filaments (Fig. 19, Pl. 
III.). A large number now began to attach themselves. Sup- 
ported on the broad end, they stood nearly erect, spinning slowly 
around. The long axis began to shorten, and by the time they 
had assumed the shape of an oblate spheroid, eight meridional 
constrictions had appeared, marking the number of mesenteries. 
The long or, rather, oral-aboral axis continued to shorten until 
the little coral had assumed a disk-like shape with a flat basal 
surface and a convex upper surface, the latter marked with the 
meridional constrictions (a transverse section of this stage is 
shown in Fig. 34, Pl. V., and a longitudinal in Fig. 38). The 
whole process of fixation occupied several hours. All the larvee 
did not become attached at the same time. On the contrary, 
many continued to lead a free life until the first part of May. 
The lot of larvze I got on the fifth of April were born in a 
more advanced state than their predecessors, and developed 
after birth more rapidly. So much so, that by the middle of 
April as many of this batch became attached as of the larvee 
born March 20. Indeed, the first fixed larvze I obtained, April 
9, were from this lot, and had taken only four days to go through 
the metamorphosis, which in all the other larve required from 
two to four weeks. This great amount of difference amongst 
the larvae, as to the time required to reach a certain stage of 
development, made it a matter of some trouble to pick out a 
