26 
that club of August last.) These gentlemen are of opinion that the 
larve spoken of are the ‘larve of the mussel and cockle respectively, 
and not parasitic. They form their opinion from finding fertilized ova 
and Bucephalus Haimeanus in all stages of growth within the same 
tubular structure, of which the generative gland consists. A dif- 
ference of opinion exists as to whether the sexes are distinct. 
Professor Huxley is of opinion mussels are usually dicecious; and 
the fact that sometimes spermatozoa and ova are found in the same 
individual is no proof of their self-fertilizing power. The same 
gentleman, in his account of the embryo, says that it is a ciliated 
neligerous larva. I haye examined the ova of fresh-water snails, and 
have seen the embryo rotating within the ovum by means of cilia. 
The surface of the body of these snails, when full grown, is covered 
with these organs, and as the adult mussel is richly ciliated, the 
inference is that the embryo would be so too. The circulation of 
the mussel is exceedlngly difficult to illustrate. The blood is 
colourless, and mixed with water from the aquiferous and water 
vascular system. A communicating vessel can be seen coming from 
the heart to the organ of bojanus on either side; the blood vessels 
from the aorta can also be seen distributed over the mantle. The 
course of the blood is therefore through the aorta into the capillaries, 
to be returned by the veins through the organ of bojanus; from thence 
to the gills, there to be Aerated, whence it returns to the heart by 
way of the branchial veins, and auricle of either side. Respiration 
is effected by two pairs of light brown branchia, floating freely in 
the lower of the two pallial chambers. They are modified inner 
folds of the mantle, connected with each other posteriorly behind 
the foot, and form a sort of partition between the anal and branchial 
chambers: that is to say, the communication between the two is not 
quite shut off. They consist of parallel tubes opening into longitu- 
tudinal canals at the base of the gills, which unite behind the 
posterior adductor at the siphonal opening. Anteriorly they are 
connected with each other at the base of the tentacles; their dorsal 
edges or bases are free. Each gill consists of two membranous 
plates, cemented together by transverse septa running across each 
tube in a slanting direction ; these form the transverse canals which 
run horizontally from before backwards. The interlaminar canal 
between the lamine of the parallel tubes, and run from above 
downwards. ‘The interlaminar and transverse canals communicate 
with each other; the canals and the outside of each bar are richly 
fringed with more than one row of cilia. The branchial currents 
carry minute particles towards the mouth, and the water is filtered 
through the interlaminar canals before it escapes. The cilia compel 
the requisite moyements of the water in the branchial chambers 
when the mussel is above water, and enable the animal to livea 
considerable time without a fresh supply. Respiration is carried on 
by the ceaseless action of these cilia, and the nutrient particles are 
