18 
Dr. Carpenter, on the Development of 
The only detailed observations with which I am acquainted,* 
that have been made upon the embryonic development of 
Pectinihranchiate Gasteropods, are those of MM. Koren and 
Danielssen on Buccinum undatum and Purpura lapillus ;\ and 
these disclosed phenomena of so extraordinary a character, 
that, if their facts and inferences are to be implicitly received, 
many of the general doctrines of development which had been 
considered to be most surely established, would need to be 
greatly modified in their application to these animals, as pro- 
bably to their congeners also. 
The singular circumstance was long since noticed by Dr. 
J. E. Gray, J that a capsule of Buccinum enclosing more than 
a hundred ova, yielded only four or five mature embryos ; and 
it was supposed by him that, as often happens in Plants, the 
great increase of some ova hinders the development, and ulti- 
mately effects the destruction, of the remainder. The condi- 
tions under which development takes place in the two cases, 
however, are so essentially different, that no parallel can be 
reasonably drawn between them. 
A similar order of facts is presented by Purpura. Each 
capsule originally contains several hundred bodies, § having 
the appearance of ova (Plate III., fig. 1); yet when it is opened at 
an advanced period, no more than from twelve to forty embryos 
are found in it ; these, however, being of such large dimensions 
(Plate III., figs. 15, 16), that their aggregate mass equals 
that of the far more numerous bodies which they replace. 
In what manner, then, are the materials of the abortive 
ova (?) applied to the nutrition of the embryos, whose 
* The Memoir of Leydig on Paludina vivipara (' Zeitschrift fiir wissen- 
schaftliche Zoologie,' 1850), referred-to by MM. Koren and Danielssen, 
has not fallen in my way. 
t ' Bitrag til Pectinibranchiernes Udviklingshistorie,' Bergen, 1851 ; 
translated in ' Ann. des Sci. Nat.,' 3ieme Ser., torn, xviii. xix. (1852-3), 
and in ' Taylor's Scientific Memoirs,' 1853. 
X ' Loudon's Magazine of Natural History,' May, 1837. 
§ In both the translations of MM. Koren and Danielssen's Memoir, 
these observers are made to state the number of these bodies as sixty or 
more. But it is evident, from the accounts which they subsequently give, 
of the coalescence of these bodies into embryos, — " some embryos resulting 
from the union of three or four ova, while sixty or more had contributed 
to form most of the others," — that this number is understated. As it is 
expressed in figures, I think it probable that a 0 has been accidentally 
omitted, and that the number should have been 600. This would cor- 
respond well with the average of my own estimates. The number is by 
no means constant, however ; the capsules varying much in size. Those 
of the same cluster, deposited by one individual, usually correspond with 
each other pretty closely ; but the ratio of capacity of those in different 
clusters is occasionally at least 2:1; and this partly accounts for the 
difference in the number of mature embryos noticed above. 
