96 TBREBBLLIDJE. 



and second segments. A single pair of branchiae ramified at their extremity and attached 

 to the third segment. Ex. T.'cristata. 



Cuvier distinguished the Terebellids by their having tubes composed of sand and 

 fragments of shells, by their bodies possessing fewer rings, the mouth being surrounded 

 by mobile tentacles, and the neck having gills in the form of arbuscles, of which most 

 have three pairs. After Savigny he used these in classification, those with two pairs of 

 gills being the T. Phyzelix, and with one the T. ldalise. 



Milne Edwards 1 (1838) gave an account of the circulation in Terebella nebulosa, 

 Montagu, and T. conchilega, Sav., which for the most part agrees with modern interpreta- 

 tions. He considered the anterior part of the contractile dorsal vessel a pulmonary heart 

 since it sent blood to the branchias ; whilst the ventral vessel chiefly performed arterial 

 functions. The contractile gills also aid in the circulation. In T. conchilega he found 

 that the lateral branches of the ventral vessel do not form rings on the upper surface of 

 the gut, but go exclusively to a vascular " locis rete " situated on each side of the visceral 

 cavity near the bases of the feet, other branches supplying the intestinal wall. 



The same author 2 (1844) examined the development of Terebella nebulosa, Mont. 

 The ova were yellowish brown and were immersed in a gelatinous mass in the tube. He 

 followed the various stages in the mucus, the assumption of the ovoid form, the appear- 

 ance of two eye-spots, the occurrence of the prototroch, and the perianal ring of 

 cilia. Then the apodous larva acquired new segments in front of the pygidium and the 

 segments were outlined. He noted the development of the alimentary system, and that 

 in two or three days the cephalic lobe was distinct, with its eyes and a median appendage, 

 whilst the ccelomic cavity had corpuscles in its fluid. By-and-by the natatory cilia 

 disappeared, but the buccal and the anal region showed energetic ciliary action. The 

 young thus differed from the adult and conformed to the general type of the Polychsets. 

 They then secreted cylindrical transparent tubes, acquired additional bristles, and hooks 

 were developed ventrally. On the eighteenth day the cephalic plate was enlarged, the 

 eyes atrophied, and there were six pairs of feet. After a time a new cephalic appendage 

 was formed— filiform, long, and furnished with "vesicules urticants," yet no blood- 

 vessels had appeared. Other tentacles followed, and whilst the larval eyes had 

 disappeared, a number of oculiform points occupied the frontal segment, and the ventral 

 scutes were distinct. When the young Terebellid had about forty pairs of feet the 

 branchias appeared, simple at first, but afterwards branched, and the blood-vessels were 

 distinguishable. At the length of 10 or 12 mm. ova were shed into the ccelomic cavity. 

 All the organs soon assumed the adult character. 



In Griffiths' edition of Cuvier's < Animal Kingdom ' (1824—33) it is stated that the 

 female part is composed of a single median ovary occupying the whole inferior face 

 of the visceral cavity so far as the ninth ring, terminating behind, according to Pallas, 

 in a bifurcation. It is composed of a great number of oviferous grains, and has a single 

 opening posteriorly. The male organs consist of four pyriform vesicles placed on each 

 side of the anterior moiety of the ovary. They open externally by minute orifices 

 between the feet. 



i < 



Ann. Sc. nat./ 2 e ser., t. x, p. 199, pi. x, fig. 1, 

 1 Oomptes Rend. PAcad. Sc. Paris/ p. 1411. 



