44 Moll. 
MOLLUSCA. 
the hermaphrodite gland. By the time the animals are 7-9 mm. long the 
organs have assumed their permanent form, except that the receptaculum 
seminis does not appear until a length of 12 mm. has been reached. The 
generative apparatus of the Stylommatophora is more primitive than that 
of the Basommatophora ; the temporarily-separated portion of the duct 
appears to correspond with the male ducts of closely allied forms ; the 
genital aperture is the homologue of the female aperture of the Bas- 
ommatophora ; the penis and vas deferens are recent acquisitions, having 
been developed since the Pulmonata separated from the main stem of the 
Gastropoda. The disposition of the generative organs, which is perma- 
nent in the Prosohranchiata , is temporary in the Pulmonata ; in these 
latter they are laid down on the female plan, and only become 
hermaphrodite by subsequent modifications. Three forms of cells have 
been found in the foot-gland of the adult. The “ sensory ” colls of 
Sochaczewer have not this function, but are the boundaries of the 
apertures of glandular cells ; these are arranged in two chief masses, one 
on either side of the efferent duct. Calcareous cells were present in the 
liver from the commencement. The foot is continuously ciliated, and 
cilia are also present in the right mantle-margin in the region of the res- 
piratory cleft ; Brock. 
Butsciilt (1) differs from Spcngel as to the mode of rotation by which 
the chiastoneural arrangement of the Prosohranchiata has been produced. 
The asymmetry concerns not only the nervous system but also the 
intestine and anus ; the latter has been displaced forwards on the right 
side in consequence of the presence of the shell. At a certain stage of 
development, while the anus is still posterior, a narrow dorso-ventral 
zone on the right side between it and the mouth ceases to grow ; the 
growth of the left side continues, and the longer this takes place the 
more is the anus displaced towards the head. The region of sup- 
pressed growth extends beyond the anus as far as the left gill, which 
thus participates in its displacement. The visceral sac also undergoes an 
independent torsion. 
Development of chromatophores has been studied in Sepiola rondeleti ; 
radiating fibres are not muscular but connective. A vesicle appears 
in the centre of a mass of yellowish pigment and coloured granules col- 
lect in it ; the cells around this vesicle are arranged radially : their 
nuclei elongate, their protoplasm forms fibrils, and their inner ends 
become continuous with the central cell. The movement of the coloured 
granules in the vacuole has given rise to the idea that the chromato- 
phores are amoeboid ; Phisalix. 
Mytilus : some further details on development are given by Wilson 
(1, 2) [cf. Zool. Bee. xxii, Moll. p. 99]. 
Growth of Loligo most marked in posterior half of body ; Hoyle, (1) 
p. 156. 
In Limnceus auricularis the fusion of the first two segments of a 
dividing egg has been observed as a pathological phenomenon by Zacha- 
RIAS. 
