214 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
10, Fig. 50, cl. gn.). Their nuclei are nearly spherical, and contain at 
least one large deeply staining nucleolus. No special preparations were 
made for the purpose of demonstrating fibrillz in either nerve cells or 
fibres. Bethe found them in all fibres, and traces of them in the cells of 
the brain. 
3. Development of the Otocyst. 
For the purpose of comparison with development in the lobster, the 
antennules of the first five free swimming larval stages of Carcinus were 
dissected out, stained and examined in toto. By this means it was 
ascertained that there is no functional otocyst in the Zoea stages. 
(a) The first Zoea shows no trace of invagination in its antennule. 
There is, however, an aggregation of nuclei beneath the chitin of the 
region where the otocyst is to appear. 
(6) The second Zoea shows a slight depression on the dorsal side of 
the antennule, and its basal portion has begun to widen. 
(c) In the third Zoea this widening has increased, and the lateral wall 
of the antennule has now formed a rounded protuberance. The invagi- 
nation has increased in size and depth, but no hairs nor otoliths are yet 
contained in it. 
(d) At the Megalops stage we find that a sudden development has 
taken place, as in the fourth larval stage of the lobster. The Zoea has 
by a single moult become metamorphosed into a Megalops, and the oto- 
cyst changed from a shallow depression to a nearly closed sac, contain- 
ing sensory hairs and otoliths. Two sensory cushions are present: one 
of these, posterior and median, bears 25 to 30 hooked hairs, upon the 
tips of which otoliths rest ; the other prominence projects from the 
anterior portion of the median wall, and bears a vertical row of about 30 
hairs, the shafts of which are directed laterally. These hairs are long, 
attenuate, and well fringed with delicate filaments. They do not come 
into contact with the otoliths, and, as already noted, they develop into 
the thread hairs of the adult ; those of the first sensory cushion described 
correspond to the hook hairs of the mature crab. The third type of hair 
found in the adult is not developed at this stage. The aperture is 
anterior and lateral in position, and extends transversely across the 
antennule. 
(e) The next stage examined was that of a young crab probably of 
the stage immediately succeeding the Megalops larva. The otocyst is 
slightly larger, and its opening is already nearly closed. As a result, only 
a few small otoliths were contained in it. 
