METAMORPHOSIS OF ACTINOTROCHA. 205 
pair of arms are seen at a”, a’, Fig. 3 is a corresponding 
view of a somewhat later stage with the first four arms now 
plainly indicated. The body is everywhere richly ciliated 
and the cilia are distinctly longer along the margin of the 
hood and at the tips of the arms. Fig. 4 represents a side 
view of a considerably later stage, with five pairs of well- 
developed, though still short, arms. A number of large 
black pigment spots have appeared. Neither the pre-anal 
belt of cilia, nor the ventral pouch, have yet been developed. 
These four figures are copied from Metschnikoff. 
The following figures represent different stages in the 
development of the two Chesapeake species, which for con- 
venience sake may be designated A and B. The two 
species have well-marked specific differences, but their me- 
tamorphoses are almost identical, and agree in the main 
with that of the form studied by Metschnikoff. A is cha- 
racterised by a very short intestine and a correspondingly 
stout body, and shows a considerable resemblance to the 
form studied by Metschnikoff (figs. 5, 7,11). B has a long 
slender intestine, and the posterior part of the body is cor- 
respondingly elongated. At the upper lateral portions of the 
stomach are two rounded glandular lobes, one on either side 
of the esophagus. The hood, in the later stages at any rate, 
has a prominent conical ciliated elevation on the median 
line in front. This form is apparently identical with Ac#i- 
notrocha branchiata, the species originally discovered by 
Johannes Miller. 
Figure 5 represents form A shortly after the appearance of 
the pouch which is seen in optical section at p on the 
ventral side. The arms are sixteen in number; they di- 
minish regularly in length toward the dorsal side, thus 
indicating the order in which they have appeared. On the 
extreme dorsal side the series is interrupted by a consider- 
able interval. The arms are nearly solid, but contain 
narrow central channels, which are diverticula from the 
perivisceral cavity. There are a number of pigment spots 
irregularly scattered over the body. The pre-anal belt of 
cilia (a. r.) has appeared, the dorsal vessel is seen at v., and 
. an accumulation of pseud-hzemal corpuscles has appeared 
at cor. on the wall of the stomach. By flattening out the 
creature under a compressor the opening into the pouch 
becomes apparent (fig. 7). 
Figure 6 represents the corresponding stage of the other 
species as seen from the opposite side, showing the pouch 
(p.) lying in the perivisceral cavity between the stomach and 
the body wall, It shows the ventral pseud-hemal vessel 
