68 
Proceedings of the Poyal Society of Edinburgh. [Sess. 
their growth. Large oocytes are very sparse in the anterior portion — in 
front of the eighth segment — but, in mature specimens, they practically 
fill the coelomic cavities of the posterior segments (fig. 5). Each full-grown 
oocyte has a thin vitelline membrane, a large amount of coarsely granular 
yolk, a vesicular nucleus, and a large nucleolus. When mature, the eggs 
are, according to Professor Mesnil, milk-white, and about ’3 mm. long and 
2 mm. broad. The volume of each egg is, therefore, four or five times that 
of the egg of any species of Arenicola. When the sizes of the parent 
worms are taken into account, the egg of Branchiomaldane is relatively 
of much greater magnitude. The marked disparity in the size of the eggs, 
is correlated with a striking difference in regard to the number of eggs 
present in mature specimens of the two genera. Immediately previous 
to the breeding season, there are many thousands * of full-grown oocytes 
in the coelom of a mature female Arenicola, but in a mature Branchio- 
maldane the number is much smaller. An almost mature specimen of 
B. vincenti was found to contain about 120 large oocytes, all in approxi- 
mately the same phase of growth; and, judging from the small amount 
of free space in the coelom, this was not far from the maximum number 
which could have been accommodated. 
The eggs of B. vincenti, being much too large to escape by way of the 
nephridia, j* can make their exit, as they do in many other Polychseta, 
only by rupture of the body-wall, which occurs in one or more of the 
posterior segments. Two of the mature specimens examined showed eggs 
escaping in this manner. 
The stages of spermatogenesis, seen in the coelom, are similar to 
those found in the Arenicola and other Annelids ; all stages, from young 
spermatogonia to masses of spermatids and ripe spermatozoa, may be 
present in the same specimen. Several of the nephridia examined con- 
tained spermatozoa. 
Professor Mesnil found eggs, in August and September 1898, around 
the mucous tubes in which the worms were living, and was able to show 
that, on hatching, the young worm has four chsetigerous segments. He 
stated that cilia were not visible on these young specimens, except at the 
dorsal margin of the prostomium, that is, in the nuchal groove. 
* The writer estimated the number of oocytes in a mature female Arenicola marina to be- 
about 80,000. 
t The lumen of the narrow tube of each nephridium, just behind the funnel, is only 
about 6 /a in diameter. 
