OPHELIHLE. 5 



lobate or pear-shaped in transverse section, and has externally a coating of tough cuticle 

 somewhat thinner than that covering the pedicle above, A distinct layer of granular 

 hypoderm, thickest near the middle line and tapering off at each side, lies on the ventral 

 surface, and thickenings occur at intervals on the upper edge near the setigerous process, 

 the powerful ventral longitudinal muscles being bent in the form of a U in each space — 

 commencing with a rounded end next the ventral muscular slip, the upper limb of the U 

 being shorter and more pointed. As in other forms the ova and perivisceral fluid 

 penetrate into the area, and the setigerous process and cirrus arise above its inner and 

 upper edge close to the pedicle. The cavity also contains the segmental organ (s. o.), 

 which apparently opens on the external border, probably in a similar manner to that of 

 Ophelia. The upper region of the body is somewhat ovoid in section with a peak in the 

 mid-dorsal line. It is enveloped by a firm cuticular coat, a granular hypoderm occurring 

 as a distinct layer beneath, and thick on the dorsal arch on each side, a still greater, 



fxv. nc o.m. 

 Fig. 99. — Transverse section of the body-wall of Ammotrypane aulogaster in the anterior region. 



though limited thickening occurring ventrally as it joins the pedicle. The extensive and 

 powerful dorsal longitudinal muscles begin on each side of the mid-dorsal line, and 

 gradually increase in bulk to the lateral region, indeed, each remains a large muscle 

 till it is slightly tapered as it touches the upper and outer fibres of the oblique muscle 

 in the pedicle. The enclosed area contains the much folded anterior region of the 

 alimentary canal, which has a corneous layer and on the dorsal arch a reticulated belt. 

 The contents of the gut include fine mud with a vast number of diatoms, radiolarians, 

 sponge-spicules, and other minute organisms. 



In the middle region of the body the pedicle — broader above and narrower beneath 

 — is considerably shorter and proportionately wider, but the other parts retain the same 

 relations. 



Claparede was of opinion that in the Opheliidas (including Polyophthalmus) the 

 oblique muscles attain their maximum development. 



The blood in the Opheliidae has rounded corpuscles, which Claparede saw passing along 

 the main trunks, but which were too large to enter the minute branches in the branchias. 

 The flattened perivisceral corpuscles show pseudopodia; moreover, some have a 



