Soe E. W. MACBRIDE. 
as a sac separate from the anterior ccelom; he states that the 
mesentery between the right and left coelomic lobes is absorbed 
ventrally. We have seen that only the posterior parts of the 
right and left coelomic lobes are employed in the formation of 
the right and left posterior cceloms respectively ; the anterior 
parts of these lobes are continuous with the anterior ccelom, 
and the longitudinal mesentery between them breaks down, as 
Ludwig observed. Hence we see that the hinder part of the 
anterior ccelom in Asterina is at first a double structure; in 
the Bipinnaria larva the anterior ccelom is at first double 
throughout its whole extent. 
At the dorsal anterior angle of the left ccelom (fig. 37) an 
invagination of its wall takes place, giving rise to a thick- 
walled vesicle (07. c.), which communicates by a narrow slit 
with the celom. This structure has been strangely misunder- 
stood. Ludwig saw it, but not its origin, and supposed it to 
arise as a ‘* schizoceele,” and regarded it as the rudiment of 
the oral blood-ring. In my preliminary account I recognised 
its true nature, but supposed that its upper end was the rudi- 
ment of the so-called heart,! with which, as a matter of fact, 
it has nothing to do. It is the rudiment of the oral celom, a 
space closely surrounding the adult cesophagus, the relations of 
which we shall study later. 
Histology of the Larva. 
The structure of the body-wall of the larva is shown in 
Pl. 27, fig. 1388, and Pl. 28, fig. 144. In the first we see 
that the peritoneum of the left posterior coelom consists of 
1 Tt will be observed that Bury, in his last paper (‘Q.J.M.S.,’ September, 
1895), makes the same mistake. This work appeared after the present paper 
had been sent in for publication, and is therefore not referred to further here. 
The best answer to Bury’s criticisms on my observations as recorded in the 
preliminary account (15) is the publication of full details in the present paper. 
Bury’s observations contain much interesting matter, but also in my opinion 
many mistakes, which are due to the fact that the stages which he obtained in 
the development of most of the larve he studied, did not form a series without 
gaps; the orientation which he adopted seems to me also not that which yields 
the best results. 
