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Proceedings of the Royal Society 
becomes constricted. In the less rigid region which succeeds, its 
wall is thinner, its cavity larger, and its connection with the body 
more lax. Its structure, however, remains the same. Food seldom 
occurs in the first region of the alimentary canal, but in the dilated 
posterior part and after it turns round to proceed forward to the 
anterior end, the granular contents abound with Foraminifera, 
Kadiolarians, diatomes, sponge spicules, and other organic debris. 
For the most part the intestine is kept in situ on the dorsal aspect 
of the first region of the canal by the oblique fibres passing from 
the dorsal wall of the body to the upper arch of the digestive tube, 
and which form, in the contracted region anteriorly, the special 
chamber formerly alluded to. The terminal portion is generally much 
contracted — except just at the anus. 
The chief point observable in regard to the circulatory organs in 
the preparations is the presence of the great dorsal trunk, which 
extends almost, but not quite, from the posterior to the anterior end 
of the body along the dorsal arch of the first region of the alimentary 
canal. It gradually increases in size anteriorly, and in the first 
or contracted division of the body frequently presents a distinct 
septum, so that there would appear to be two channels, as in 
Magelona. A great lateral sinus occurs on each side, within the 
body-wall, at the termination of the dorsal trunk, but the exact 
mode of communication with the branchial vessels has not been 
observed. On each side of the main (or first) division of the 
alimentary canal is a considerable lateral trunk, and many large 
branches occur in the spaces between the body-wall and the former, 
being especially conspicuous in the interstices of the radiating fibres 
in the anterior region, and at the tip of the tail, — after the great 
dorsal and lateral trunks disappear. Many small vessels are apparent 
beneath the primary division of the alimentary canal, but no large 
trunk occurs in that position. .None of the vessels are so small as 
to merit the name of capillaries, and all are loaded with large 
circular granular cells. 
The generative apertures occur on each side of the anus, on a 
lateral elevation which appears just beyond the chitinous elements 
of the branchial apparatus. These apertures pass into a capacious 
chamber. The ova are developed in the posterior region of the 
body in racemose masses above the chief division of the 
