Biology of Fabia subquadrata — PEARCE 
17 
1958 1959 
Fig. 3. Curves showing per cent of total crab population constituted by: solid line broken by circles, ovig- 
erous Stage V females; solid line broken by crosses, nonovigerous Stage V females; dash line broken by circles. 
immature crabs of both sexes. Samples collected from San Juan Channel off Point Caution, San Juan Island. 
Washington between August 8, 1958 and November 23, 1959. 
upwards of eight weeks in attaining the first true 
crab stage. Hart (personal correspondence) has 
recently reared F. subquadrata. She found that 
eggs laid on October 27, T9 58 hatched on Febru- 
ary 6, 1959 and moulted into the first true crab 
stage on April 6, 1959. As already discussed, it 
is assumed that the first crab stage enters an 
initial bivalve host, usually Modiolus modiolus, 
and completes a series of prehard moults which 
culminate in the hard, Stage I instar. This is true 
both of the male and of the female. It is sus- 
pected that in general the prehard series occu- 
pies the interval between early April and late 
May. At this time the Stage I crabs leave their 
hosts and engage in the swarming activities 
which culminate with copulation. Following 
these activities the Stage I female, and at least 
some males (since larger Stage I males occur in 
the collections throughout the remainder of the 
year ) , return to a bivalve host, where the female 
undergoes a series of at least four posthard 
moults which terminate in the definitive adult, 
the Stage V crab. 
The immature posthard and Stage V crabs re- 
tain the full spermathecae which result from the 
precocious copulation of the Stage I instar. Non- 
ovigerous Stage V females are present in the 
greatest numbers during August, September, and 
October, and this is the period when the num- 
bers of immature crabs are sharply decreasing. 
During late October and early November the 
ovigerous females become more numerous and 
once again, during mid-winter, they constitute 
the majority of the population. 
There is a period of three months between 
the time the Stage V crabs are first found in 
increasing numbers and when the ovigerous 
females are noted to represent a significant por- 
tion of the population. Furthermore, since many 
Stage V crabs are found moulting during this 
period one may assume that at least one or two 
moults will occur in this period. This assump- 
