198 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
of curvature is different for different hairs. The larger, being in a mcre 
elevated position, usually bend at a sharper angle than those near the 
floor of the sac. All are heavily plumed ; the pinnules are long and 
coarse (Plate 7, Fig. 31, pinn.) and often have otoliths firmly attached 
to them by a substance probably of glandular origin. Hensen (63) 
describes the otolith hairs of Crangon, as follows: ‘Es steht nimlich auf 
die schon erwihnten Vorbuchtung eine einzige Reihe von 7 oder 8 
Haaren ; diese Haare reichen bis zur Kugel in die Steine hinein, thre 
Zahl erscheint viel zu gering fir deren Masse. . . . Sie sind 0.075 mm. 
lang, 0.0075 mm. breit und gerade anfgerichtet.” 
This description of these hairs is completely at variance with the 
conditions I have found in the American Crangon. In order to deter- 
mine, therefore, whether this was a true specific difference, or due to an 
error on Hensen’s part, a number of the European specimens, procured 
by Dr. Mark from Professor Herdman in Liverpool, were examined. 
After dissecting out the otocysts of 12 specimens, I was entirely satisfied 
that Hensen’s description was incorrect. The hairs are precisely the 
same in size, form, and number as in the American variety. They have 
their shafts distinctly bent near the tip at angles varying from 25° to 90° ; 
of the individuals examined none possessed less than twenty-four hairs 
in the sac, the average being twenty-six. 
That Hensen should have made such a mistake is not strange. He 
himself says: “their number appears much too small for the mass [of 
the otoliths].” The tips of the hairs are concealed by the otoliths, and 
only the first third of the row would be visible from above. 
d. The formation of hairs after ecdysis is identical with that of 
Palzemonetes. 
e. The otoliths are numerous, larger than in Paleemonetes, and found 
mostly in the posterior part of the sac, in contact with, or even attached 
to, the fringed tips of the hairs. Mainly siliceous, they are taken in 
after each moult, being readily pushed into the large opening of the 
otocyst. They can be almost completely washed out by a fine jet 
of water introduced artificially, and if the animal so treated is then 
placed in an aquarium containing iron filings, or other substitute, this 
material will soon be used to replace the otoliths of sand. 
2. Innervation of the Otocyst. 
As in Paleemonetes, the brain is very close to the otocyst, and the 
nerve supplying the sac is therefore short. Its general course is shown 
at n. ot. in Figure 29 (Plate 6). 
