Mayeb. — Staurocephalus gregaricus. 



PLATE 1. 



Fio'. 1. Staurocephalus gregaricus, nov. sp., natiiral size, swimming near the sur- 

 face of the water before the rising of the Sun. The terminal segment 

 has broken off, and the genital products are escaping through the 

 orific^e. 



Fig. 2. Staurocephalus gregaricus, natural size, showing the worm in the act of 

 expelling its sexual products. The eggs or sperm escape into the 

 water througli the nephridial tubules, and also through rents and tears 

 in the cuticula of the worm. This contraction usually occurs immedi- 

 ately after the rising of the Sun. 



Fig. 3. Side view of the head end of the worm ; magnified, {m) mouth. 



Fig. 4. Setae of the parapodia. (a) are most dorsal ; (b) next; (d) next; and (c) 

 most ventral. See Figure 13, Plate 2. 



Fig. 5. Section of an embryo in the 16-ceIl stage, magnified 100 diameters. Age 

 3 hours. 



Fig 6. Section of an embryo in the gastrula stage immediately before the closure 

 of the blastopore, (bp) blastopore; (sgc) segmentation cavity. Age 

 9-J hours. 



Fig. 7. Longitudinal dorso-ventral section of an embryo .S^ days old, magnified 

 100 diameters. (a;i) p'^ite where the anus is destined to appear; (17/) 

 head glands ; (m) place wiiere the mouth is destined to break through ; 

 (oes) oesophagus, (st) mid gut, or " stomach." The egg-membrane 

 persists as a larval cuticula. 



Fig. 8. Longitudinal dorso-ventral section of a young worm 16 days old. (an) 

 anus; (r/s, (/.>;, etc.) dissepiments; {(/I) head glands; (in) mouth; (»i) 

 ventral nerve-chain ; (oes) cesophagus ; (st) cavity of mid gut. 



Fig. 9. Longitudinal dorso-ventral section through the liead region of a mature 

 worm, showing tentacular cirrus and muscular pharynx. The intes- 

 tine of the sexually mature worm is practically empty, (m) mouth, 

 (n) ventral nerve-chain. 



