ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
161 
homologous with the cerebral ganglia of Molluscs, but that these centres 
rather correspond to the lateral oesophageal ganglia of Neomenia. Struc- 
tures homologous with the small oesopbageal ring of Solenogastres are 
found in Annelids, Chiton, Haliotis, Dentalium, and 3Ieleagrina ; there 
are no anterior visceral ganglia in Solenogastres or Annelids, but they 
are to be found in all true Molluscs, except Lamellibranchs. 
Horaologues of the sensory organs of the lateral line of Chgetopods 
are to be seen in the sensory organs found at the edge of the mantle of 
Lamellibranchs and in the epipodium of the Ehipidoglossa, while the 
gills of Chitons are derived from homologous cirri. It is in agreement 
with this that the ganglia of the lateral organs of Chsetopods, the nerve 
of the edge of the mantle of Lamellibranchs, and the ganglia in the 
epipodium of the Ehipidoglossa are homologous with the lateral cords 
of the Amphineura, while the two ventral pairs of ganglia of Lamelli- 
branchs, the anterior of which is the centre for locomotion, and the 
posterior for the protection of the animal, and the pedal ganglia of 
Gastropods correspond to the ventral cords of the ventral medullae of 
Annelids. 
It will be noticed that a distinction is drawn between the ventral 
cords, and the lateral cords and cerebral ganglia ; this is justified by 
their modes of innervation, and largely also by the histological structure 
of the centres ; the ventral cords and their homologues correspond, in 
their general characters, to the dorsal medulla of the Chordata. 
a. Cephalopoda. 
Tract of Modified Epithelium in Embryo of Sepia.* — Mr. W. E. 
Hoyle has found a trifid tract of peculiarly modified ectodermal cells 
near the posterior aspect of the body of embryos of Sepia. The three 
ridges are clearly visible by the naked eye in embryos 5 to 8 mm. long, 
and seem to have been noted by Kolliker who, however, gives an 
incorrect account of their origin, llie cells are larger in all dimensions 
than those of the adjacent epithelium, so that the level of the body is 
slightly elevated where they are present ; the contents of the cells are 
finely granular, and stain more deeply than those of the normal epi- 
thelium ; the cell-boundaries become indefinite towards the superficies, 
and, in some cases, this part of the tract stains more deeply than the 
rest. 
The presence of a similar organ has been observed in embryos of 
Loligo and OmmastrepJies, but in them the median portion only was seen. 
The function of the patch is probably glandular; as to its homology the 
author can only suggest the shell-gland and the iuvaginated gland which 
has been described as existing at the posterior extremity of Sepiella. 
Innervation of Arms of Cephalopoda. f — Sig. G. Jatta maintains 
the pedal nature of the Cephalopod arms, inasmuch as the brachial 
nerves originate, according to his investigation, from the pedal ganglion, 
to which the brachial ganglion may be considered accessory. 
* Proc. Roy. Pliys. Soc. Edinb., x (1889) pp, 58-60. 
t Boll. Soc. Nat. Napoli., iii. (1889) pp. 129-32, 
1890. 
M 
