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Mr. E. W. MacBride. 



[Dec. 7, 



My results diverge from those of Ludwig at this point. What 

 follows is the result of my own work. The coelom becomes segmented, as 

 shown in fig. 1, and the arrangement of its divisions strongly recalls that 



ph - 



Fia. 1. Diagram of a Longitudinal Horizontal Section through, a late Larra of 



Aster ina gibbosa. 



of Balanoglossus. By the outgrowth of a pair of vertical transverse 

 septa, a pair of posterior coelomic cavities is separated off (3' 3', fig. 1), 

 this separation being for a time incomplete ventrally. Simulta- 

 neously, two outgrowths from the anterior cavity appear, growing 

 backward, and overlapping to some extent the posterior cavities. Of 

 these, the left opens for a long while by a wide aperture into the 

 anterior cavity, whilst the right is almost immediately completely 

 segmented off. 



These are the paired rudiments of the water- vascular system, the 

 right and the left hydroccele. In one larva I found them equally de- 

 veloped, but usually the right hydroccele has the form of a small 

 closed vesicle, which persists for life in the neighbourhood of the 

 madreporite. These cavities I compare to the collar cavities of 

 Balanoglossus, and find support for this view in the structure of 

 Cephalodiscus, where the collar cavities are prolonged into long, 

 pinnately -branched arms, comparable to the radial canals of the water- 

 vascular system of Echinoderms, with their rows of tube feet. 



There is no hcemocoele in Asterina gibbosa ; all cavities lined with 



