DR. E. B. WILSON ON THE DEVELOPMENT OF RENJLLA. 
729 
perhaps because they are younger and less mature. The ovaries of polyps which had 
recently spawned were usually found to contain considerable quantities of immature 
eggs. Hence it seems probable that there may be several successive broods of egg 
in a single year, since the spawning season extends over two or three months. 
It is a rather curious fact that the eggs are always laid at very nearly the same 
hour of the day, viz., about 6 A.m. Large numbers of Renillas were kept in aquaria, 
and the act of spawning was several times observed. In a single case only the 
spawning took place as early as half-past five and it was never observed to occur later 
than 7 a.m. This regularity appears to be independent of temperature, although this 
has a very important influence on the rate of development; for the hour was the same 
on cold and warm days. It is not unlikely that marine animals are more regular in 
such habits than has been suspected. A similar case is that of Lucifer, which, as 
Dr. Brooks has observed, deposits its eggs always at the same hour, viz. : from 
9 to 10 p.m. 
During the discharge of the eggs by the females the males pour out the spermatic 
fluid in a milky cloud rising from the colony. The male element is apparently 
discharged, like the eggs, through the mouths of the sexual polyps. The sper¬ 
matozoa are of the ordinary tailed form with pyriform heads, and swim with great 
activity. Fertilisation is effected in the water. 
When first discharged the eggs are usually more or less distorted by pressure 
during their passage through the oesophagus; within a few minutes, however, they 
become perfectly spherical, and have an average diameter of about '35 mm. They are 
of stony opacity, so that the germinal vesicle is invisible, and are destitute of any 
proper limiting membrane, though the peripheral layer of the vitellus is clearer and 
less granular than the rest. The entire substance of the vitellus is densely packed 
with deutoplasm granules, which upon rupture of the egg appear as clear yellowish 
spherules. Polar cells were never observed. 
It will be convenient to describe first those changes which are visible from the 
exterior, leaving to the next section an account of the corresponding internal changes 
as discovered in sections. In a third section a review of the facts will be given, 
together with a discussion of their significance. 
The segmentation of the egg in Renilla is remarkable for the surprising amount of 
individual variation of which it is capable. So great is this variation that it is safe to 
say that no two eggs ever develop in precisely the same way; and although most of 
the variations may be arranged in a definite series, some of them are so irregular that 
they seem to follow" no definite law. No one indeed without actually following the 
entire development of some of these eggs would suppose them capable of normal 
development. For a long time, in fact, I passed by some of the less usual forms as 
due to abnormal or pathological changes, and only after repeated and careful study 
was able to convince myself that these peculiar embryos gave rise to active larvae, 
