ANATOMY AND PHYSIOLOGY. 
Moll . 39 
Bavay (J. de Conch, xxiv. p. 383, 188 0 records that Helix cooperi is 
viviparous. Further notes on the same subject; II. hasmastoma has an 
egg 17 mm. by 12 mm. : Fischer, t. c. p. 384. 
Mytilus edulis is bisexual, maturity occurring in April ; McIntosh 
( 242). 
In Clio borealis, three individuals, not merely two, are necessary to 
copulation ; Wagner (373). 
10 . Embryology. 
McMurrich (245) has observed a postoral band of cilia in several 
Gastropod embryos, and summarizes the possible phylogenetic history of 
the group thus :— u They and the Annelida have had their origin in a 
Trochophore. In the Gastropods this ancestor developed a univalve shell, 
represented by the larval shell, so often replaced, as development pro¬ 
ceeds, by another. . . . The development of this shell, by increasiug 
the specific gravity of the animal, rendered the simple prseoral cilia of 
the Trochophore insufficient for active locomotion, and the extent of the 
band was increased by the region of the body on which it occurred being, 
as it were, pulled out laterally, the characteristic velum being thus pro¬ 
duced.” 
Larva of Paludina is a Pilidium, that of Teredo a Trochosphere. The 
body, both in Annelids and Mollusks, “ is the highly-developed oral lobe of 
the Trochosphere. The shell of the Mollusk arises on the surface of the 
body, equivalent to the dorsal surface of the Annelids. The velum is 
simply a larval organ, but the part of the body within its area is equi¬ 
valent to the cephalic lobe of the Annelids, or the proboscis of Thalas- 
sema. In both Mollusks and Annelids, therefore, the oral lobe elongates 
at the expense of the preoral lobe, but the resulting body in one case 
covers itself with a shell, and^ in the other becomes segmented.” 
Conn (84). 
The cilia in Molluscan embryos, whilst in the egg, serve to increase 
the inception of oxygen and saline solutions through the egg-membrane ; 
many details are also given regarding the motion ; Preyer, Spec. Phys. 
ties Embryo, pp. 385-391. 
The early stages in the development of Fissurella exhibit no peculiari¬ 
ties. Below the rudimentary velum is a prominence indicating the 
future foot, and between these the rudimentary mouth, and opposite 
them the invagination for the shell. The shell shows traces of the twist- 
iug characteristic of Gastropoda. The larva at this stage is remarkable 
for the position of the foot, which is situated between the velum and 
the mantle, a condition rectified by a gradual process of torsion. The 
larva is now four days old; the velum is bilobed ; but the digestive 
tract is not yet differentiated. Two prominences appear near the 
middle of the velum (tentacles) ; the foot bears an operculum and two 
ciliated appendages. The shell is still coiled, and covers the dorsal part 
of the embryo ; the otoliths are visible, as is also the digestive tract. 
The larva now quits the glairy mass in w T hich it was previously em¬ 
bedded, and crawls by the foot, rarely swimming. It is now about three 
1885. [vol. xxii.] c 6 
