88 
F. ERNEST WEISS. 
(2) thinks that such a form regularly losing its long arms 
points to the way in which the Octopoda gradually developed 
from the Decapoda. 
The eyes are not pedunculate, nor indeed prominent. 
Behind the eyes is a small patch representing the olfactory 
sense organ, and connected by a nerve with the main cerebral 
mass (fig. 2, olf. org.). 
Sections taken through this organ show a cushion of many- 
layered epithelium cells, some oval and some spindle shaped, 
and sunk away from the surface, and supplied with nerves from 
the ganglion, which lies beneath the cushion. They resemble 
greatly the sensitive cells figured and described by Sochaczewer 1 
(13) in the pedal gland of the Snail. The cilia, if present, are 
very short ; probably there are only sensitive hairs, and not cilia 
proper, which would be unnecessary, as the surface is exposed 
to the free play of the water. Mucous cells seem absent. 
I take this to represent the simplest form of cephalic 
olfactory organ in Cephalopoda, as in sections of embryos of 
Loligo and Ommastrephes I have found this patch with 
similar modified cells situated in about the same position 
behind the eyes. Indeed, on a surface view of a young 
Ommastrephes it forms a very conspicuous elongated knob 
laterally and posteriorly to the eye. 
In the nearly related form Enoploteuthis this organ is more 
prominent than in Yerania. 
In Onychoteuthis it is represented by a ridge, and when we 
get strong cervical ridges developed as in Thysanoteuthis, we 
find it, as mentioned before, as a small lappet in the corner of 
the partition formed by these ridges (PI. X, fig. 7). 
In Ilistioteuthis, where these ridges become much reduced, 
the lappet seems relatively larger but occupies the same posi- 
tion ; and this form leads on to Chiroteuthis with its spoon- 
shaped organs, and Doratopsis with its stalked and club- 
shaped processes. 
Unfortunately sections across the processes in Histiotcuthis 
and Chiroteuthis do not reveal any modified epithelium cells 
1 Sochaczewer, ‘ Zeitschrift fur wiss. Zoologie,’ 1881. 
