MOLLUSCA. 
that of Buccinum undatum , except that it has no operculum ; the head has 
well-developed, slightly flattened tentacles, the left being the larger. The 
formula of the radula is 1, 1, 1. The centres of the nervous system are 
very condensed ; the branchial is further removed from the cerebral 
than in Buccinum ; which, however, it resembles in being chiastoneural 
and not orthoneural, as stated by von Jhering. The author is disposed 
to place this animal, in spite of the lack of an operculum, among the 
Buccinidce. 
The epidermis of Dentalium is a simple epithelium ; at the two ends of 
the mantle unicellular glands are found in it, which secrete the shell. 
The nerve-ganglia are composed of a grey cortical and white medullary 
substance; the former consists of unipolar cells, the latter of fibres 
without neuroglia. The muscles are composed of smooth fibres, disposed 
like those of Verteh'ata, but having a denticulate appearance, due to 
trabeculae of protoplasmic substance which connect each fibre with its 
neighbour. An elongated nucleus may be found in each fibre. There 
are two layers of circular muscles in the foot, surrounding longitudinal 
bundles, with transverse bundles crossing a large sinus in the axis of the 
foot. The buccal tentacles are hollow, and communicate with the vascu¬ 
lar system, but not with the exterior. The alimentary canal is lined by 
epithelium of varying character, cylindrical or glandular. The liver and 
kidneys are digitate hollows, lined with epithelium; the two halves of 
the kidney are connected by a common median pouch below the anus, 
and open externally by the aperture described by Lacaze-Duthiers ; no 
internal opening was seen. The blood-sinus has a pair of openings to 
the exterior, with sphincter muscles. On the surface of the ovary there 
are young ovules, the greater part of which is occupied by the nucleus. 
These enclose a double nucleolus which disappears in the mature ova. 
The efferent genital canal described by Lacaze-Duthiers was not seen, 
and it appears most likely that the products are discharged by dehiscence 
through the anal gland, or perhaps by way of the pallial cavity or kidney ; 
Fol (130). 
Leydig (232) refers the presence of pores in the calcareous tissues and 
muscles of Ancylus to physical forces, and not to the vital action of the cells. 
The direct division of the nucleus by constriction seems to be the most 
usual. Red colour of oesophageal cartilages apparently connected with 
subaqueous existence. Ancylus has upon the head, and especially on the 
tentacles, stiff bristles, resting on special bases. The author is convinced of 
the existence of intercellular spaces in normal tissues, but does not believe 
in a water-vascular apart from the blood-vascular system. The muscular 
elements exhibit a differentiation into cortical and medullary substance. 
See also Bergh (15,16) ; and Fischer (125, 126). 
1 . Shell, Integument, and Connective Tissue. 
Gumbel (150) has investigated the resistent powers of various portions 
of shells by placing them in water through which carbonic acid gas was 
passed for some weeks. Under these circumstances the compact parts 
were dissolved more rapidly than those less closely aggregated. This 
