4 MOLLUSCA. 



The hard or soft albuminous capsules, or ootheco'^ which 

 defend and protect the ova of molluscous animals, offer 

 a variety of forms. The eggs of the Cephalopods are 

 either agglomerated into masses like bunches of grapes, 

 as in the Cuttles, or into long garlands and strings, as in 

 nearly all the Squids. The ova of marine Gasteropods 

 are enveloped before exclusion in mucous capsules, in some . 

 cases soft, flexible, and transparent, which harden more or 

 less by contact with the water, and assume forms peculiar 

 to tribes and genera. This nidus or egg-nest is some- 

 times simple, but often compound, each compartment 

 containing many ova. In Mazza the cells are of a 

 flattened sub-pentagonal form, adhering together and piled 

 one upon the other, each compartment containing from 

 twenty to thirty embryos. The ootliecce of Purpura Jkr- 

 mastoma are yellow or rosy, elongated, quadrangular, and 

 truncate at their ends, and are fixed in groups upon 

 the rocks. The nidus of P. lajyillus, which Ellis calls 

 the sea-cup, is in the form of an elliptical vase supported 

 on a short stem. The egg-capsule of Neptunea Norve- 

 glca is attached, isolated, hemispherical, with a thin, 

 coriaceous membranous coat. In Buccinum widatum the 

 nidimental capsules are aggregated in large irregular 

 masses, each case being oblong, one side convex, the 

 other flat. The nidus of I^assa reticulata is in the form of 

 a compressed pouch, with a short peduncle and an opening 

 at the top. The small nidimental cells of the cowry 

 are aggregated in a flattened group. In Bursa they 

 are in numerous groups very close together, long, com- 

 pressed, enlarged at the end, with one or two keels. 

 In TropJmi they are sub-cylindrical and truncate at 

 the upper end, and deposited in groups on stones and 

 fuci. 



