320 GASTEROPODES. 



The spawn is discharged by the parents in some variety, as a line, a 

 rope, a coil, a curve, or a spiral, the finest of pure gelatinous consistence. 

 Perhaps nothing visible is intermingled with the finest ; but on almost all, 

 exposed to observation, are innumerable minute corpuscula. Besides the 

 examples already dispersed throughout this section, I propose to add a 

 few more illustrations, which, although very obscure in themselves, may 

 satisfy some queries of the curious. I could have wished they had been 

 more explicit as well as more numerous. 



Originally these corpuscula are the merest specks, hardly to be disco- 

 vered by the acutest vision. But,, armed with the microscope, we find them 

 becoming more distinct with the lapse of time. They evidently advance 

 from an earlier to a later stage, acquire the faculty of motion, and at 

 length, escaping the prison wherein they are confined, reach strength and 

 maturity to swim in the surrounding element. 



Thus we behold the connection of the Nautiline with the Doris. It 

 exists in the spawn, but here our knowledge terminates. No resem- 

 blance, not the most remote, can be traced between the Nautiline and 

 the parent of the spawn it has quitted. Its form is permanent ; it does 

 not shew the slightest tendency to metamorphosis ; it undergoes no sen- 

 sible change whatever, and it may be said to die exactly in the same 

 shape wherein it was born. 



If, by losing some parts and acquiring others, it approaches to 

 maturity, this change is accomplished while beyond the cognizance of the 

 naturalist. If it could be beheld in the sea., there is no means of following 

 its courses, and, as disappearing, of recognizing it again. Thus there is 

 no possibility of connecting the two. 



The extreme minuteness of the Nautiline forms our main obstacle 

 to the prosecution of its history. None of its parts, and scarcely the 

 whole, can be distinguished by the naked eye ; and, under the microscope, 

 those of all different species seem almost identically the same. 



But, we can say that there is certainly a body contained in a shell 

 of a particular shape ; that the body seems to consist of a sac, containing 

 subordinate organization below, with two hollow cylinders, on which 

 vibrate marginal cilia. All those parts appear tolerably distinct ; yet we 



