390 E. W. MACBRIDE. 
larve of Stage D, and saw the completely closed ccelomic 
vesicle on the right, and the imperfect transverse septum on the 
left side, and was at a loss how to interpret these appearances ; 
the right hydrocele he calls a mesenchymatous vesicle. 
It is curious to see how unable many zoologists have been to 
grasp Bury’s idea of the anterior celom; thus Seeliger, who 
has confirmed his work on Antedon and amplified it till it 
may be said that we have an exhaustive knowledge of the 
subject, objects to consider the structure Bury named anterior 
ccelom as such, on the supposition that Bury meant by that a 
fellow of the hydrocele, which it obviously is not. Seeliger 
calls it the “parietal canal,’ but the structural facts he so 
accurately relates are convincingly in favour of Bury’s inter- 
pretation. The weak point in Bury’s observations on Plutei 
and other larve was that in no case were any more than a few 
stages taken at random examined; but I hope the account I 
have given in this paper will provide a more solid basis for the 
idea of segmentation of the celom in Echinoderms. Field (5) 
has published a short paper on the development of the Bipin- 
naria; he carries it up only to a stage corresponding to midway 
between Stages B and C of Asterina. The chief points of 
interest in the paper are that many of the larve had two 
madreporic pores, and he suggests that this is a normal stage 
in the ontogeny; also that the two ciliated rings characteristic 
of the Bipinnaria are derived from one, and that there is a 
preoral sense-organ comparable to that in Antedon. 
This paper does not contain the discovery that the water- 
vascular rudiment is paired; for, as a matter of fact, in the 
oldest larva examined no trace of the left hydroccle was 
present. The “ schizoccelic space,” near the madreporic pore, 
may represent the rudiment of the right hydroceele; needless 
to say, it was not recognised as such. 
Theel (22) has recently succeeded in following the meta- 
morphosis in Echinocyamus pusillus so far as the external 
features are concerned. He finds that already in the blastula 
M. Russo’s technique was obviously not equal to dealing successfully with 
such difficult subjects as Kchinoderm larvee. 
