in the young of the Gasteropodous MoUusca, S;c. 123 



body, and consequently the shell, to assume a curved form, 

 with the heart always on the convex side of the curve. The 

 heart pulsates about twenty times in a minute, and the dias- 

 tole of its cavities is much more sudden and remarkable than 

 the systole. If the motions of the heart were the only powers 

 which turned the body from a straight line, the spire of the 

 Buccinum would revolve on the same plane round its shut ex- 

 tremity, like that of a SpirorUs ; but as the animaPs foot re- 

 quires continually to descend over the columella of the shell, 

 before it can reach a solid surface to creep upon, the body 

 and the shell are thus incessantly deflected from the original 

 plane, and forced to assume the spiral form which we observe 

 in the adult Buccinum, and in most univalve shells. In the 

 reverse shells, where the cone lies on the left side of the ani- 

 mal, we likewise find the heart in a reverse situation, being 

 then on the right side. The two wide projecting circles of 

 cilicB at the sides of the mouth continue visible for some time 

 after the escape of the young Bufcinum from the general cell, 

 and they are of such length and size that their motions can 

 be easily followed by the eye aided by the microscope. The 

 young of the Purpura lapillus are also inclosed in a horny 

 general capsule, like those of the Buccinum. The ovum of the 

 Purpura is shaped like a grain of corn, while that of the Buc- 

 cinum is flat like a split pea. When first deposited, the horny 

 covering in both is white and soft, but soon becomes yellow 

 and firm, and the transparent gelatinous matter enveloping 

 the young becomes gradually thinner as the young advance 

 to maturity. There are about fifty-five young in each cell of 

 the Purpura, and they exhibit the same mode of develope- 

 ment as those of the Buccinum; the same revolution of particles 

 within the transparent part of the embryo give the first indi- 

 cation of life, and the same wide ciliated opening is seen on 

 each side of the head, the dlicB continuing to vibrate for some 

 time after the escape of the young from the cell or ovum, as 

 in the Buccinum. 



These circles of long vibrating cilicB I have also met with 

 in the young of other genera of testaceous mollusca, as the 

 Trochus, Nerita, &c. which are not inclosed in a general horny 

 cell, but are merely enveloped in a soft gelatinous matter, by 

 which they adhere to the leaves oifuci till they arrive at ma- 



