OVIPOSITION AND CHARACTER OF THE EGG-CAPSULES AND EGG. 103 



cleavage, some of the embryos, however, develop no further, but 

 perish, their remains being devoured by the other embryos. This 

 is also the case, according to McMuRRiCH, in a few species of 

 Cf'ititltila, and in Uroxa//nn.<- (BROOKS). Fa^'iolaria lays about 200 

 eggs in each capsule, but only 4 to 6 of these develop, and this is also 

 the case with Bucdnurn unduftum. Kaeh capsule of Pur/>'u- lapillus 

 contains 400 to 600 eggs, only 10 to 16 of which develop into mature 

 embryos (SEL.ENKA). The egg-capsule of X^ritina fluviatili* also 

 shelters a large number of eggs (according to BLOCHMANN 70 to 90) 

 although only a single embryo in it attains complete development 

 (CLAPAREDE). In this case, the unfertilised eggs divide soon after 

 the polar bodies have formed, and break up into irregular heaps of 

 protoplasmic spheres, being in this way distinguished from the eggs 

 undergoing cleavage. 



In shape and structure, these egg-capsules vary greatly. As a 

 rule they are formed of tough leathery or parchment-like integument 

 and are in some cases approximately spherical, but appear flattened 

 on the side by which they are attached to foreign objects. This is 

 the case in Nerlfiii'i. the older cocoons of which easily divide into 

 two hemispherical halves. To allow the brood to escape, the capsule 

 occasionally has an aperture closed by a delicate membrane, situated 

 opposite to the point of attachment. Several capsules are usually 

 found together, as in ttw.rinum undnt urn 9 Futsutt antiqnus and others, 

 the capsules of which are piled one upon another, thus forming an 

 enormous mass of spawn. They occasionally appear laterally com- 

 pressed and, in one species of FH*H>* observed by BOBRETZKY, are 

 round plano-convex discs, attached by the flattened side. The 

 capsules of /Jntsycon (Fu/yur) also are leaf-like or rather disc-shaped ; 

 these are arranged in a row like a roll of coins, and are attached to a 

 common filament. These capsules have an aperture opposite to the 

 points of attachment for the escape of the brood. 



In AWx.svf iiHitabitiiSj the capsules are cup-shaped and attached by 

 the obliquely truncated end, the opposite pointed end carrying an 

 M pert ure at first closed by a membrane. The surface of these capsules 

 shows polygonal markings which form rib-like or membranous ridges. 

 They are found united into large clumps on sea-weeds and worm-tubes. 



The cup-like capsules of many Prosobranchia are arranged in 

 groups attached by their narrow ends drawn out into stalks (Murex). 

 Here also, the aperture of the cup is closed by a membranous cover, 

 which opens when the brood is ready to hatch. In Pw/mm l(i\iill^ 

 10 to 15 such capsules, which, however, are more flask-shaped and of 



