MOLLUSCA. 269 



colour therefore appears uniform, except that a clear Hue 

 runs round just within the edge, caused by a narrow space 

 free from eggs. The ova, although numerous and close- 

 set, occupy only the central portion of the band, there 

 being a considerable space of transparent jelly without them 

 on each surface. On the 19th of March I cut off a small 

 piece of the ribbon of spawn and examined it beneath a 

 microscope; I found that the young were fully formed, 

 each enclosed in a globular egg, perfectly transparent and 

 colourless. The young Doris, unlike the adult, vThich is 

 a naked Slug, inhabits a transparent shell, formed like that 

 of the Nautilus, from the mouth of which project two large 

 fleshy circular discs, set round with long cilia. These 

 latter organs were in constant and vigorous vibration, by 

 the motion of which each little animal revolved freely in 

 its egg-shell, incessantly turning upon its centre in every 

 direction. Sometimes one would suddenly suspend the 

 motion of its cilia as if tired; then, after having rested a 

 few moments, put forth one cilium in a cautious manner, 

 then another, and in a moment the whole were again in 

 vibration, and the little embryo was gyrating in its giddy 

 dance." 



