GASTEEOPODES. 293 



They came into mutual contact, as they were seen tumbling over each 

 other. The integument of the capsule must be inconceivably thin, from 

 its transparency. It is doubtful whether, of these four Nautilines con- 

 tained in a capsule referred to, each is confined in its own peculiar inte- 

 gument. Plate XLIII. fig. 7. 



This great deposit, obtained on the 12th of February, was chiefly 

 dissolved and broke up on the 1st of March ; and numbers of the Nauti- 

 lines were observed floating at the surface of the water. 



All this was of no avail, however, in determining whether the spawn 

 had been produced by the argo or verrucosa ; though the subjects afford 

 good illustrations of the general nature of the Doris. 



It is not easy to obtain a satisfactory microscopical view of the com- 

 position of the prolific ribband, and it would be vain to attempt computing 

 the multitude of the offspring from a single individual. 



The propagation of this animal is not confined to any particular 

 season, though more common in the earlier part of the year. Vast 

 numbers of young have been matured from spawn produced in March. 

 Multitudes of the Nautiline formed a whitish scum on the surface of the 

 water of a vessel, which, exposed to the microscope, proved partly those 

 creatures, partly their empty shells. It should be understood, that the 

 shells are simple cavities ; they contain neither chambers nor partitions. 

 When occupied, the animal appears wholly grey, with several internal 

 sacs or solid organs ; also a transparent vessel, of considerable size, con- 

 taining a colourless fluid, wherein dark globules are suspended and car- 

 ried about, as if around the interior circumference. All Nautilines exhibit 

 two external circular spots, apart, on the middle of the front, which cer- 

 tainly denotes two organs in the earliest stage. 



Although this be the most common of the tribe, often dwelling little 

 within low water-mark, and occurring of very small dimensions, I have 

 never met with it, or with any other so minute, or of such form, as would 

 indicate transition from the Nautiline. Perhaps it feeds on the algae and 

 the fuci. It is of the most sluggish nature, and actually becomes agglu- 

 tinated at last to the surface whereon it reposes. 



This species is prone to quit the water. 



