454 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
of development (fig. 53, O'.) can be seen attached to the 
wall, but gradually projecting more and more as they 
increase in size until they are set free in the cavity 
(fig. 08, O.). 
The ova are large cells about 0°05 mm. in size, and 
when lying in the alveoli are polyhedral in shape. The 
nucleus is very large, spherical or oval in shape, and about 
two-thirds the diameter of the cell. A delicate network 
is present, extending over the nucleus, and in addition, 
they are small granules staining with eosin, and a 
conspicuous nucleolus. ‘This is situated close to the 
periphery at one side of the nucleus. In some cells more 
than one nucleolus is present, there being often a large 
and two smaller ones at its sides. 
The cytoplasm is granular and dense, and around the 
ovum is a prominent vitelline membrane which leaves an 
opening—the micropyle, at the poimt where the egg 
remained last attached to the epithelium of the alveolus. 
The spermatozoa (fig. 53, S.) are rather small and of 
the typical shape; im fixed preparations the head is oval 
in shape and stains very intensely. From the middle of 
the broad end a long flagellum arises. In the alveolus 
the tails of the spermatozoa are generally all directed in 
the same way towards a point in the centre or nearer one 
end where the duct opens, whilst the heads are directed 
towards the wall of the alveolus. Both spermatozoa and 
ova travel along the same gonoducts to the exterior. 
EMBRYOLOGY. 
I have been unable to obtain enough specimens of 
P. maaimus sufficiently ripe at the same time to artificially 
fertilise the eggs, but hope to continue this work 
at some future date. It has been already pointed out 
