112 MOLLUSC A. 
4. Directly and openly connected with the supra-cesophageal ganglion. 
a. By a long nerve in the Heteropoda : Carinaria and Firola. 
b. Sessile in JEolis. 
Although it is not yet proved by experiment that these oto- 
cysts are really the special organs for hearing, there can be 
scarcely any doubt that they are so, from their anatomical rela- 
tions. Arch. Z. Par. i. pp. 97-166, pis. 2-6. 
E. R. Lankester adds to these observations, that in the Nadi- 
branchiata the auditory capsule develops from the cells of the 
outer layer of the embryo, and in the Cephalopoda by an intru- 
sion of the outer layer, the orifice of the cavity so formed eventually 
closing in, and its neck remaining as the curious little ciliated ap- 
pendage described by Kblliker. O. J. Micr. Soc. (2) xii. 
p. 418. 
W. Flemming (Arch. mikr. Anat. vi. 1870, p. 410) and Jobert 
(J. de PAnat. 1871, p. 611) also discuss the feelers and the epi- 
thelium of the sensitive organs in i\i(d Mollusca', the former (Z.wiss. 
Zool. xxii. pp. 369-371) states further that the large cells on the 
inside of the skin of the feelers and body, figured in his first 
paper, are really ganglionic cells, and that epithelial warts, 
crowned with rigid hairs, have been observed in large numbers 
on the head, on the edge of the mantle, and on the filaments at 
the sides of the foot in Trochus cinerarias (L,), These may also 
be specific sensitive organs. 
In some remarks on the development of various genera of Pro- 
sobranchia (3rd meeting of Russian naturalists at Kiew, and Z. 
wiss. Zool. xxii. pp. 285-289), Prof. Ganin states, in opposition 
to Gegenbaur, that no bending of the heart, or coalition of an 
anterior and posterior aorta, or of two atria, takes place. Dr. 
Salensky considers there are two distinct types of development, 
in one of which {Cahjptrcea^ Nassa, and probably most Cteno- 
branphia) the velum is developed very late, and some primordial 
provisory organs occur, which afterwards disappear, and in the 
other [Trochus J and probably the rest of the Aspidobranchia) 
the velum is one of the first formations, and no such organs 
occur. Prof. Kowalevsky thinks that the mantle of the MoU 
lusca may, on account of its development, be homologous with the 
embryonal envelope of the Insect a. 
The mathematical form of the spiral shell is the subject of an 
Inaugural Dissertation by A. H.Grabau [vide supra) 
reviews former publications on this subject, and comes to the 
conclusion that, although Naumann does not sufficiently consider 
errors arising from the difficulty of accurate observation of the 
inner whorls, or of the determination of the right mathematical 
line in tuberculated or plaited shells, yet his term concliospiraP' 
is a more adequate expression for the spiral line of many shells 
than logarithmic spiral, adopted by others and formerly by 
