NEREIS PELAGICA. 279 



On the 28th March three Heteronereids were procured at the margin of the beach, 

 near high water-mark. They swam swiftly and gracefully through the water. No 

 sperms could be observed in the vessel, which contained a large quantity of water. 



In contrast with the condition in this species it is interesting to find that in the 

 Japanese Geratocephale osawai of Izuka, 1 the epitokous form presents no marked change 

 in the structure of the feet though they increase in size, and develop swimming bristles. 

 Moreover, a considerable region posteriorly shrivels even before swarming, and is cast 

 off by the pelagic anterior moiety, which discharges its sexual elements by the ruptured 

 posterior end. The distension of the anterior region of the epitokous Nereis pelagica. 

 and the more slender and mobile posterior region with its modified feet thus foreshadows 

 the condition in the former. 



Habits. — Like other Nereids this species in confinement forms tough tubes of 

 secretion on the sides of vessels, and the same habit occurs in the early stages of the 

 epitokous condition. 



Development. — The development of Nereis pelagica is still in need of further elucida- 

 tion, though it probably closely corresponds with that of other forms, such as N 

 Dumerilii and N. diversicolor — indeed, the very early stages may have been confounded 

 with these. In the bottom -net at the beginning of November many small ova of a dull 

 yellowish hue, and larvae of the same tint rotating by aid of cilia, are captured, but 

 their relationships are doubtful. By transmitted light the larvse are yellowish green. 

 Externally are more minute cells, within are globules of yolk. 



A young Nereis pelagica of forty bristled segments and measuring 8 mm. was 

 obtained at Lochmaddy in August. In this the tentacles are larger in proportion 

 than in the adult, whilst the tentacular cirri are shorter. The longest (in spirit) 

 extends to the fourth segment. The eyes are wider apart and have the long axis 

 longitudinal. The bristles, though small, and with indistinct camerse, appear to follow the 

 normal type. This is probably the young of the year, just as another procured at St. 

 Andrews in September probably is. The latter has forty-four bristled segments. The 

 eyes are more rounded. Attached to the twenty-eighth foot on the right is a parasitic 

 body of a clavate outline (like a Demo&ex) with traces of segmentation and apparently a 

 chitinous cuticle (Plate LXXI, fig. 7 i). 



An older form with fifty-seven bristled segments was procured at St. Andrews in 

 May and it probably represents the young of the previous year, as also does a somewhat 

 larger form brought from deep water the same month. The lobes of the feet in these 

 are proportionally more elongate than in the adult. 



Similar young in tubes are common in deep water and they show long tips to the 

 heterogomph bristles. 



At Lochmaddy in August an example with sixty-three bristled segments was found, 

 measuring about 1 in. in spirit. Such may have been hatched very early the same year, 

 but this diagnosis is uncertain, for it is possible that it may have belonged to the 

 previous year. 



1 ' Journ. Coll. Sci. Univ. Tokyo/ vol. xvii, art. ii, 1903; also ' Ann. Nat. Hist./ ser. 7, vol. xv, 

 p. 35. I am indebted to the author for excellent examples of this form. 



