of the Fishery Board for Scotland. 
291 
After the discharge of the generative products, the organ is in a collapsed 
condition, and exhibits a light brown or cream colour. When, however, 
the reproductive tissues become active, the flabbiness disappears, and the 
organ increases in size, the colour changing with the increase in size. The 
testes become white and opalescent, while the ovary assumes a reddish 
tinge. The colour of the latter becomes more pronouuced, passing from 
a pale red to a bright scarlet, and often a rich vermilion. Sometimes the 
opalescence of the testes persists, but generally these become cream coloured 
on the ripening of their products. .During this alteration in colour of the 
sexual organs they gradually pass in shape from the collapsed rounded 
form to a knee-shaped form, flattened laterally; this form, flattened laterally, 
lills up so that in transverse vertical section its ellipsoid shape becomes at 
some parts nearly circular. 
The products of the generative organs in the same individual do not 
ripen at quite the same time. When the ova are ready to be shed, the 
spermatozoa have either been shed, or they are not quite ripe. Some 
have been found with ova quite ripe and spermatozoa not ripe, while the 
converse has also been the case. The interval, however, that separates the 
ripening of both is not many days at most ; in some scarcely has the one 
organ collapsed when the other immediately succeeds. 
As Lacaze-JDuthiers* has noticed, the generative products do not pass 
directly to the external medium, but into the organ of Bojanus. He 
figures the generative duct in P. varius and P. glaber, as opening into 
the auterior end of the cavity of the organ of Bojanus, but in P. opercularis 
{</.d.), so far as made out by the injection of coloured fluids, the openings 
are not always quite so far forward, nor are they so distinctly seen as in 
P. varius. The hermaphrodite duct runs for a short distance alongside 
of the organ of Bojanus, and in some cases at least opens into the organ 
of Bojanus between the anterior extremity and the middle of that organ. 
The external and common opening (k.o.) for the discharge of the renal and 
generative products is at the posterior apex of the organ of Bojanus, and can 
easily be found either by puncturing the walls of the organ of Bojanus, 
and inflating it, or by using tlie blowpipe close to the posterior apex, when 
the rush of air into the organ reveals the presence of the external opening. 
From the organ of Bojauus of either side (the organs are quite separate) 
the common generative duct runs backwards for a short distance close to 
the surface of the testes, and theu divides into two branches, one of which 
ramifies chiefly in the testis, while the other branches for the most part in 
the ovary. The canals repeatedly divide and redivide, and the course of 
these, on the surface especially, is easily traceable by employing coloured 
iujections. While one of the two main canals functions principally as an 
oviduct, and the other as a vas deferens, yet small branches of each convey 
also products of the other sexual organ to the cavity of the organ of 
Bojanus. The postero-dorsal branches of the hinder of the two main canals 
are exclusively oviducal, while the anterior or sub-hepatic branch of the 
main testis-canal is entirely spermatic, but many of the smaller canals 
between these act as both oviduct and vas deferens. 
The reproductive products are apparently discharged at once to the 
exterior, for after often repeated examinations of sexually mature forms I 
was unable to find in the organ of Bojanus, or even within the valves of 
the shell, either ova or spermatozoa. Fertilisation therefore must take 
place in the surrounding water, and the dispersion of the generative 
products is well provided for by the continual flapping motion of the 
valves even in gravid specimens. 
* "Organes Genitaux des Acephales Lamellibranches, " Ann, de. Sc. Nat., Ser. iv. 
torn. i. 
