284 
NOTES AND MEMORANDA. 
The Optic Bod in the Crustacea and Annelida. — Tlie following are 
tlie “ conclusions ” of M. J oannes Cliatin, in his article on this subject 
in the ‘ Annales des Sciences Naturelles ’ (Zoology), 6th series, vol. vii. 
p. 31 : — 
“ In attempting to sum up the principal results, we see that the 
optic rod of the Crustacea presents general characters which are con- 
stant in the whole class, and also arrangements either S2)ecial or of 
variable importance which differ according to the types examined. This 
should suffice to show the danger of the method too often followed, 
and according to which the observation of a few insects may furnish 
results capable of being immediately extended to the whole of the 
Arthropoda. 
Limited externally by the ‘ cornea,’ terminating internally in the 
ganglion of the optic nerve, the rod presents two very distinct parts, 
of which the characters as well as the importance differ notably — the 
one, internal and more or less slender, deserves more especially the 
name of rod ; the other, external, short and swollen, but of variable 
shape, is the cone. 
It is needless to recall here the general characters of the latter, 
and the signification of the central line in which it has been attempted 
to show the analogue of the filament of Eitter ; but as far as regards 
the rod, I insist particularly on the value which it is proper to attribute 
to its transversal striae, which do not in any way indicate a contractile 
tunic, but are proper to the rod which may be separated into a certain 
number of disks thus marked out. This disposition establishes a 
close relationship between the optic rod of the Articulata, and the rod 
of the Vertebrata.^ 
Such is, in short, the structure of the rod in the generality of the 
class ; if we go back to the different types studied, the principal forms 
which it there presents can easily be recalled. In Astacus, Squilla, 
Pagurus, Eupagurus, and Paguristes, rods are met with, whose con- 
stitution is really higher, as many details show. The Cypridina 
offer analogous dispositions, but seem, however, to tend towards a 
close histological simplification ; this is particularly marked in 
Typton, and more clearly still in Lysianassa, where the rod shows no 
transversal strias and the cellules of Semper are represented only by a 
dark spot, from an early period of development. 
Notopterophorus and Caprella scarcely differ from the types last 
studied, but as much cannot be said of Epimeria, in which the organie 
degradation is marked in a considerable degree, and leads to extremely 
simple forms which in Lichomolgus become still more rudimentary. 
This rapid outline reminds us of the manner in which the study 
of the Crustacea has led us progressively to more and more simple 
bacillary elements. Moreover, and without wishing to enter here 
into the discussion of the theories to which I allude, we know the 
important part which many contemporary zoologists accord to the 
existing too heterogeneous series of Worms, whose ensemhle would 
constitute a kind of ‘ groupe de depart ’ allied by a close affinity to 
* It is known that the researches of Boll have recently confirmed my own 
observations. 
