138 



SYLLKLE 



constriction. Body terminated posteriorly by two cirri, sometimes with an intermediate 

 papilla. The minute feet have dorsal and ventral cirri, or the latter are absent, are 

 uniramous, and bear falcate bristles with a terminal process, which is either simple or 

 bifid. Swimming dorsal bristles also occur in the sexual forms. 



Grube describes the stolones as having few segments, two or three tentacles, two 

 palpi, with tentacular appendages and tentacular cirri ; two eyes, generally large. Feet 

 with two fascicles of bristles ; bristles in some compound, in others simple and long. 

 Cirri present or absent. Proboscis and proventriculus absent. 



The chief features of the body-wall (Fig. 49) in such species as Syllis armillaris 

 is the proportionally large size of the dorsal longitudinal muscles, which form in trans- 

 verse section a massive arch resting, as it were, upon the broad base formed by the 

 incurvation of the lower edge. A slight median raphe carries the mesentery from the 

 gut. Externally are the circular fibres, the very thin hypoderm, and lastly the thick 

 cuticle. The arrangement of the fibres of these and the ventral muscles in transverse 

 section corresponds with that of other families, such as the Nephthydidge. The ventral 

 muscles approach each other very closely in the median line, a condition, however, which 



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vm 



Fig. 49. — Muscles of the body-wall of Syllis armillaris (Miiller) (Erst., as seen in section. 



does not appear to be general in the group, so that the nerve-cords are pushed upward, 

 only a pedicle, apparently of basement-tissue, connecting them with the external 

 hypoderm. The oblique muscles pass below the cord to be attached to the raphe in the 

 intervals. 1 Another feature of interest is the presence of a strong muscular slip — from 

 the fan-like muscles of the spines — which goes straight downward at intervals through 

 the ventral longitudinal muscles to the basement-membrane. As slips from the bases of 

 the spines pass dorsally along the inferior border of the dorsal longitudinal muscles, and 

 on the other hand, ventrally along the outer border of the ventral muscles, the movements 

 of the spines and of the foot with its bristles are well provided for. 



Though De Quatrefages did not observe blood-vessels in the Syllidas, Ehlers, 

 Claparede, De St. Joseph, Viguier, and Albert found them, the latter describing dorsal 

 and ventral vessels, a branch to the dissepiment, and a caecum in the middle of the 

 genital gland. Malaquin showed that the dorsal and the ventral vessels communicated in 

 the cephalic region by a double loop. Such is, briefly, the condition in the Syllides and 



!• Claparede (1868) mentions that the Syllids have a large tubular fibre on the dorsal surface of 

 the nerve-chain. This has not yet been observed in the British forms. 



