178 FLORENCE BUCHANAN. 



On the same segment (the Ist)^ placed ventro-laterally, 

 almost vertically below but a little behind each branchia 

 (fig. 1), is another group of three or four rather longer capil- 

 lary chsetaBj behind and below each of which is a membranous 

 lobe — the ventral " cirrus " of most authors, the neuropodial 

 " lamina ^^ of others. 



The body of the first segment reaches further forward on 

 the ventral than on the dorsal surface, and is there folded, 

 forming a kind of ventral collar (figs. 1 and 3, v. coll.). 

 This fold can be traced up laterally to the base of the branchiae, 

 which appear to be attached to it. 



Thoracic and Abdominal Regions. — On all the other 

 segments of the body there are, as on the first, two groups of 

 chsetse on each side, but the chaetae are longer (when of the 

 same kind) and more numerous than on the 1st segment. 

 Their number varies in different individuals and in diflferent 

 segments of the same individual, but with no constancy. 

 Five, six, and seven are usual numbers, but sometimes there 

 are as many as nine in a group. Seeing that they may so very 

 easily be knocked off, and that new ones may always be form- 

 ing, not much importance can be attached to their exact 

 number in difi'erent segments and in difi'erent individuals. 

 In the dorsal groups throughout the whole length of the body 

 the chaetsp. are capillary only (fig. 4, a.). In the ventral groups 

 they are so also in the anterior region of the body ; but from 

 the 8th segment onwards there are, as well as these, also 

 hooked or crotchet chaetae. We may, therefore, consider the 

 thoracic region to extend as far as the 7th segment (in- 

 clusive), and the abdominal region to begin in the 8th. There 

 are at first two or three crotchets to about four or three 

 capillary chaetae. More posteriorly there are usually about 

 five hooked chaetae to two capillary ones. Each crotchet (fig. 

 4, c.) is three-toothed at the extremity, the one tooth being 

 larger and more prominent than the other two, so that in 

 some views it alone is to be seen clearly (fig. 4, c.'). The 

 hooked extremity is surrounded by a membrane. 



I The name " cirrus " would imply a homology with the cirrus of the 



