770 



PROFESSOR J. STEPHENSON 



rounded tip. There are no eyes. Many of the specimens were undergoing asexual 

 multiplication ; and of the others, some had only recently separated, as evidenced by 

 the partially developed condition of the anterior ventral setae. 



Setae. — There are no dorsal setae in the anterior part of the body in the fully 

 developed animal ; they begin in segment xviii, xix, or xx ; and each bundle consists 

 of one hair- and one needle-seta. Minor variations in the constitution of the bundles 

 occasionally occur ; thus the hair-seta may be absent, or there may be two needles 

 in a bundle. 



The hair-setae are about 150 m long, and 3 m broad at the base ; they taper to a 

 fine point. They are straight, or with a very slight sickle-shaped curve. 



Text-fig. 1. — Setae of Hccmonais laurentii. x 540. a, anterior ventral ; b, posterior ventral ; 

 c, single-pointed ventral ; d, dorsal needle ; e, single-pointed dorsal needle ; /, genital seta. 



The needles (text-fig. 1, d) are of the usual doubly-curved and double-pronged type. 

 In length they are about 105 m, in breadth 4*5 m ; the curves of the shaft are gentle, 

 and the whole distal extremity is less hooked than in the ventral setae. Of the two 

 prongs into which the distal end forks, the distal is longer and may be slightly 

 thinner than the proximal, but both prongs are absolutely much longer than those of 

 the ventral setae. The angle between the prongs is narrow. The nodulus is distal to 

 the middle of the shaft, the proportion of the distal and proximal sections of the 

 shaft being about 3:5. 



There is a considerable amount of variation in these dorsal needle-setae ; thus the 

 relative length of the two prongs to each other is variable, as also the position of the 

 nodulus, which may be nearer the middle of the shaft than is indicated above. They 

 are largest and most typical in the posterior part of the body, where they may reach 

 115 m in length. But the most striking variation is the not infrequent absence ol 

 one of the two terminal prongs (text-fig. 1, e). It appears to be the distal prong 

 which is missing ; this is, usually at least, indicated by the presence of a slight 

 " shoulder " on the shaft, as shown in the text-fig. 



The ventral setae, of the type usual in the Naididae, occur in bundles of from two 



