GASTEROPODES. 305 



tion, considered it a real lid. I cannot presume to assent to this, as it 

 might be some disproportionate part of the organization protruding, to 

 be subsequently modified. Fig. 17. When it was withdrawn, or the lid 

 closed, and the Nautiline quiescent, the figures resembled the object in 

 fig. 18. 



But there are so many illusions ready to deceive the observer, in 

 contemplating such difficult and unintelligible objects also with two 

 different intercepting media from view that he can never speak too 

 diffidently regarding them. 



The true colour of these creatures seems white ; their shells are 

 remarkably smooth and shining, which is best seen in a number floating 

 together at the surface of the water, apparently unable to descend. 



Among those at the bottom of the watch-glass, were some corpuscles 

 of uncertain nature, like a dark spherical ovum, with a transparent coating. 



The Eolis dwells in society. I have scarcely ever found it solitary. 

 It is one of the few whose food is known, which renders it a favourable 

 subject for observation ; and, as the young grow readily and rather 

 speedily, a progressive evolution of their external organs may be satis- 

 factorily investigated. 



PLATE XLV. 



FIG. 7. Eolis sanguifer. Back. 



8. Belly. 



9. Spawn. 



10. The same, enlarged. 



11. The same, more enlarged. 



1 2. Spawn of reddish colour. 



13. The same, enlarged. 



1 4. Nautilines in the spawn. 



15. Nautilines, free. 



16. Nautiline, more enlarged. 



17. Another, with the lid. 



18. One with the apparent lid closed. 



2Q 



