452. TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
found that when the ova were quite ripe the spermatozoa 
had either been shed or were not quite ripe, some being 
found with ripe ova and sperms not ripe and others just 
the converse. ‘The same applies to P?. maartmus, and the 
difference in the time of maturity of ova and sperms 
cannot be more than a few days. 
Specimens of P. opercularis with ripe gonads have 
been obtained at all times of the year on the scallop beds 
in the Firth of Forth, the maximum of reproductive 
activity being, however, in July and August. Pecten 
mavimus has been dredged off Port Hrin with ripe gonads 
in December, April, May and throughout the summer, 
and in the same condition off Belfast Lough in February 
and March, so that the reproductive activity extends at 
least over the greater part of the year. 
The gonads have one opening on each side into the 
renal organ, situated near the pericardial end, at the 
level of the prominence on each side of the visceral mass 
near the attachment of the lower ends of the inner labial 
palps. The ducts can be traced im serial sections, and 
although the opening cannot be made out in dissections, 
it is possible, by pressing the ripe gonad, to force the 
products out into the renal organ, though care must be 
taken not to force them through one of the veins leading 
from the visceral mass, which may be easily mistaken for 
the oviducts. ‘The products of the gonads must be poured 
directly into the sea through the renal organ, and thus 
fertilisation takes place externally. 
The gonad consists of many branched tubuli (fig. 58, 
Go.d.), bearing numerous almost spherical sacs, the 
alveoli (fig. 53, Go.al.s. and Go.al.o.). The sexual 
products, spermatozoa or ova according to the position, 
arise by the proliferation of the cells forming the germinal 
epithelium on the walls of the alveoli. As the gonads 
