MONTACUTA. 213 



fortable quarters from which it had been extracted. In 

 a short time it protruded the mantle beyond the shell, 

 extended its large foot, and began to crawl about." And 

 as to the fry he says, " After having kept my specimen 

 for some days in sea-water, I found one morning that 

 the bottom of the glass was covered with a minute 

 white dust, which I immediately concluded would be 

 the spawn, and on placing a small portion under the 

 microscope I found that such was the case. I sub- 

 sequently had it removed into a separate glass with a 

 fresh supply of water, in order to observe its develop- 

 ment. Though nearly round at first, the ova soon 

 assumed a subtriangular shape, and about the third day 

 strong cilia were observed on one of the sides, and they 

 began to rotate very quickly. One after another assumed 

 the rotatory state, till nearly the whole were in motion. 

 After rotating for about a day, they apparently burst 

 the envelope, and swam freely about in all directions 

 by means of their vibratile cilia, and at the same time 

 assumed more or less of a bell- shape a slender style 

 or thread projecting from the centre of the ciliated base. 

 This organ, which has been observed in the embryos of 

 other species, has been described as a kind of byssus, by 

 which the little creature can fix itself securely to other 

 bodies. This, however, I did not observe to be the 

 case in the present instance. It soon appeared to be 

 absorbed ; the animal became gradually elongated, and 

 the cilia were withdrawn into the shell, which then 

 began to appear; but at what time it was actually formed 

 I could not make out, as, from its extreme transparency 

 and similarity of colour to the rest of the animal, it was 

 very difficult of detection. The cilia could be seen 

 vibrating within the shell for some time after the ani- 

 mal became quiescent a few isolated cilia at one of the 



