MOLLUSCA. 297 



received with some qualification. The living examples 

 of Janthina which I have irritated when they have 

 been confined in a vessel containing sea-water have 

 not emitted any of this coloured fluid ; when taken in 

 the hand they would sometimes allow a little to exude ; 

 but the entire quantity obtained from one animal by 

 artificial means was never sufficient to cloud or obscure, 

 although it would stain, about half a pint of pure water. 



The spawn of Janthina is attached to the under 

 surface of the float, in the form of numerous small 

 oval sacks, each suspended by a short slender thread. 

 Some of the ova have a delicate pink or flesh-colour, 

 while others are dark-brown a difference that de- 

 pends, probably, upon their state of maturity. Over 

 some extensive tracts of ocean, especially in lats. 7 

 and 29 N., we found vast quantities of the floats, all 

 all of them loaded with ova, scattered on the surface of 

 the water, and not attached to either animal or shell. 

 It is difficult to account for this fact upon the supposi- 

 tion that any accident could have destroyed the fish and 

 shell but left the floats entire ; we are therefore com- 

 pelled to admit, that these spawn-bearing appendages 

 are cast off by the Janthina as a mode of propagating 

 its species ; which necessarily implies that the parent 

 animal must, for some time, sacrifice its essential 

 buoyancy and sink to some depth beneath the surface 

 of the sea, until a second float is formed by the foot. 



In common with other molluscs floating passively on 

 the ocean, the Sea-Snail is exposed to the caprice of 

 currents, on which, indeed, it must chiefly depend for 

 any material migration. Hence, we often find great 

 numbers assembled in very limited tracts of water, 

 where they serve to indicate the previous or present 

 existence of a current. The highest latitudes in which 



