1 ^4 Dr Grant on the existence and uses of cilice, Sfc. 



turity. In such genera as have the ova enveloped only in a 

 soft gelatinous matter, we find a delicate membrane surround- 

 ing each foetus^ and inclosing a thin amniotic fluid. In these 

 the ciliCR are so long, and so rapid in their motions, that the 

 young are seen within the ova revolving continually round 

 their own axis, by striking the cilicB against the inside of the 

 containing membrane; and when they escape from the ova, they 

 are carried with great velocity through the water by the vibra- 

 tions of the cilicB. I have observed the same appearances in 

 the young of the naked gasteropoda as in the ova of different 

 species of Doris, Eolis, &c. which are inclosed in a soft trans- 

 parent gelatinous matter, and adhere by it to rocks or other 

 solid marine bodies. The young in these genera are likewise 

 surrounded, each by a thin membrane and amniotic fluid. 

 They are seen almost continually revolving round their centre 

 within the ova, and they swim rapidly forward by the action 

 of their cilice when they escape from the ova. In those ge- 

 nera which deposit the young in a general horny cell, as those 

 first described, we find no membrane or amniotic fluid sur- 

 rounding esLch Jcetus, but the horny covering is lined with a 

 delicate membrane which incloses the whole of the embryos 

 and the gelatinous fluid in which they are developed. The 

 young of the Buccinum, when mature, escape from the cell, 

 by a part of the horny covering separating on the inner con- 

 cave side of the cell. The young of the Purpura escape by 

 the falling off of a firm gelatinous plug from the free extre- 

 mity of the cell. The portions of the outer covering which 

 fall off are probably loosened by the motions of the young 

 -within ; and as the young are still safely lodged in their cells 

 when they first come in contact with the sea water by the for- 

 mation of the aperture, we find the cilice in such genera much 

 less developed than in the other genera without a horny co- 

 vering. Their motions appear destined to bring a constant 

 supply and renewal of pure sea water in contact with the 

 young in the cells, in order to perfect the formation of the 

 shell before their final departure from the now open cavity 

 of the cell. In the ova which are enveloped in a gelatinous 

 connecting matter without any horny covering, we observe 

 that connecting matter become very soft and loose, and se- 

 parate into long flocculi when the young have arrived at 



