4380 A. J. NICHOLSON 
Finally, we may consider the cases in which ‘ yolk nuclei’ 
form part of the nutritive mechanism. It is evident that this 
collective term includes several distinct types of structures, 
and 1 will only deal with one of these, the Corpuscles of Bal- 
biani. The origin of this body is obscure in most types which 
have been examined, but Chubb (4) shows very clearly that 
in the oocyte of Antedon this body arises in the nucleolus 
as a series of deeply-basophile spherules which are passed 
into the cytoplasm. These form a mass just outside the 
nucleus, and eventually they fuse to form the yolk nucleus. 
McGill (19) describes a similar aggregation of granules close 
to the nucleus in the oocyte of the dragon fly, and this gives 
rise to the yolk nucleus. Though she has been unable to 
demonstrate the origin of the granular mass she shows that it 
is very probably nuclear in origin, and in support of this theory 
remarks that ‘ Hennegay (18938) believes that the Corpuscles of 
Balbiani in Vertebrates are either parts of the nucleolus or the 
entire nucleolus which passes through the nuclear wall into 
the cytoplasm ’. 
Similarly Bambeke (1) observes that the ‘corps vitellin’ 
of Pholeus phalangioides arises close to the germinal 
vesicle, and he considers that it is nuclear in origin. He shows 
that this grows into a large and somewhat branched structure 
which takes an active part in the nutrition of the oocyte. 
This structure bears a considerable superficial resemblance 
to the branched nucleus of A. maculipennis, and a careful 
consideration of Bambeke’s very excellent paper has led me 
to the conclusion that the resemblance is not merely superficial 
but that the two structures are both morphologically and 
physiologically comparable. It should be noted here, however, 
that Chubb (4) considers that the yolk nucleus of Antedon 
has no connexion with yolk formation though it is almost 
identical in every respect with the yolk nucleus of Pholeus. 
He gives a perfectly simple physical explanation for the 
changes undergone by this structure, which he regards as waste 
material forming a purely passive body. 
We have seen that the branched nucleus of A. maculi- 
