706 American Work in the Department of [September, 
ology, a statement of the nature, method and extent of the 
observations and conclusions reached from them, with a few 
words of warning in relation to the inevitable ruin of the beds to 
follow excessive dredging ; the laws relating to which, it may be 
noted—though Professor Brooks does not mention it—are practi- 
cally ignored. He finds the average number of eggs in an oyster 
of ordinary size to be about nine million, against less than two 
million reported for the European oyster; while some American 
oysters may furnish sixty million. In the European, however, 
the young are believed to be protected, during their most preca- 
rious stages, in the parent shell, so that perhaps z3$a0 Of them 
come to maturity, while our American species undergo their 
development in the open sea, subject to fatal changes of tempera- 
ture and unnumbered enemies, which must greatly diminish the 
proportion of survivors. The sex of individuals during the 
breeding season, contrary to the oystermen’s opinion, cannot be 
distinguished without dissection, and they appear, for the time 
being at least, to be singly male or female only, and never her- 
maphrodite. 
The second part of the paper discusses some of the more ab- 
struse topics connected with the subject, and is written more for 
the embryologist, as the former part is for the general reader. 
Among the conclusions arrived at, are the singleness of sex in 
the individual ; that the impregnation is external to the shell; 
that the segmentation is remarkable for its rapidity ; its bilateral 
symmetry and marked alternation of periods of rest and peri 
of repose; both regular and rarely-recurring irregular processes 
of segmentation are described, and the conclusion is reached that 
the process of Lamellibranchiate segmentation is a survival from 
ancestral conditions which included few large eggs provided with 
food-yolks, these last having been lost as the eggs became 
smaller and more numerous, while the mode of segmentation has 
been retained perfectly by the oyster and incompletely by other 
Lamellibranchs, The evidence appears to the author to strengthen 
his previously expressed opinion that the Lamellibranchs must 
be regarded as aside branch from a main stem, of which the 
Gasteropods are a much more direct continuation, and that the 
phylogeny of the higher Mollusca cannot be traced through the 
Lamellibranchs to lower invertebrate forms. Of these views, the 
second paper on the acquisition and loss of a food-yolk (with a 
