50 



MANUAL OF THE MOLLUSCA. 





like the parent as to have been described and named by natural- 

 ists as distinct species; — these solitary salpians again produce 

 chains of embryos, like their grand-parents. {Chamlsso.) 



Oviparous rep'oductlon. The sexes ai*e distinct in the most 

 highly organised (or dicecious) mollusca ; they are united in the 

 {monoecious) land-snails, pteropods, brachiopods, tunicai'ies, and 

 in part of the conchifers. The prosobranchs pair; but in the 

 dicecious acephalans and cuttle-fishes, the spermatozoa are merely 

 discharged into the water, and are inhaled with the respiratory 

 currents by the other sex. The monoecious land-snails require 

 reciprocal union ; the limneids unite in succession, forming float- 

 iug chains. 



The eggs of the land-snails are separate, and protected by a 

 shell, which is sometimes albuminous and flexible, at others cal- 

 carious and brittle ; those of the fresh-water species are soft, 

 mucous, and transparent. The spawn of the sea-snails consists 

 of large numbers of eggs, adhering together in masses, or spread 

 out in the shape of a strap or ribbon, in which the eggs are ar- 

 ranged in rows ; this nid a mental ribbon is sometimes coiled up 

 spirally, like a watch-spring, and attached by one of its edges. 



The eggs of the carnivo- 

 rous gasteropods are in- 

 closedin tough albiuninous 

 capsules, each containing 

 numerous germs ; these 

 are deposited singly, or in 

 rows, or agglutinated in 

 groups, equalling the parent 

 animal in bulk (fig. 70^. 

 The nidamental capsuli s 

 of the cuttle-fish are clus- 

 tered like grapes, each 

 containing but one embryo ; those of the calamary are grouped 



rig. 29. Spawn of Doris." 



Nielaineiital ribbcn of Doris Johvstoni. {Alder and Hanccck.) 



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