THE DEVELOPMENT OF THE CAPE CEPHALOD1SCUS. 191 
further stage, which is free-swimming, and in which the 
five body cavities may be recognised. He regards the central 
mass of yolk in the embryo and larva as representing an 
endoderm formed by involution. Braem (1911) draws a 
comparison between this free-swimming larva and that of 
certain Polyzoa. Harmer (1915) draws attention to the 
different disposition of the body cavities, and gives a summary 
of the points in the development of Cep halo discus on 
which there appears to be unanimity, drawing attention to 
the unexplained origin of the gastrula-like stage. 
There are, as will be seen from this review, several 
important gaps in the development of Cep halo discus 
which have not yet been filled up, and on which further 
information is very desirable. Thus, nothing is known of 
what occurs between the first segmentation stages and the 
gastrula — this alleged gastrula requires further investigation ; 
the exact mode of origin of the body cavities has not been 
explained ; and finally, the metamorphosis of the larva into 
the adult still remains to be elucidated. 
The chief points on which the present work seems to throw 
further light with regard to these questions are : Segmenta- 
tion stages leading to the formation of a blastula, which does 
not become invaginated to form a gastrula, but develops into 
a solid body, the outer parts of which become differentiated 
into an ectoderm and endoderm, the main inner yolk mass 
not representing the endoderm, nor its cavity the arch enter on ; 
the origin of the body cavities, the anterior as a part parti- 
tioned off from the archenteron, and the posterior as a lumen 
internal to the developing endoderm. 
Ovary and Ovarian Egg. 
The structure of the ovary of this species has been briefly 
described by Ridewood (7). It consists of a very narrow 
oviduct, leading into a mass of developing eggs in which no 
distinct lumen can be made out. The great majority of the 
eggs are comparatively small, one or two, at the point furthest 
