252 NEREIDS. 



products, and in which the feet acquire foliaceous lobes and swimming bristles. Again 

 in some the males at maturity present a varicose or serrated condition of the dorsal 

 cirri, whilst the females show this in a slighter degree or not at all. Dignet mentions that 

 in Mav, 1901, in the Gulf of California he found male Nereids in which the body was 

 composed of three regions, the anterior characterized by the enormous development of 

 the dorsal cirri, which formed powerful natatory organs; a middle region with ordinary feet 

 and cirri, and a posterior division in which the feet were metamorphosed for the epitokous 

 condition. The eyes were very large and encroached on the ventral border, and the 

 palps much reduced 1 (Gravier). 



The comparatively great size of the ova of Lycastis quadraticeps, Gay, from Chili 

 and Punta Arenas, in the Strait of Magellan, as described by H. P. Johnson, 2 is a feature 

 of interest in this small species, for they are about half the diameter of the body, and, 

 moreover, the species is hermaphrodite. It frequents not only the sea, but brackish and 

 even fresh water. 



In Nereis Dumerilli young forms may become ripe whilst still Nereids, or they may 

 assume the Heteronereid condition during the ripening of the sexual elements; and as 

 the larger Heteronereids frequent the bottom whilst the smaller are pelagic, there are thus 

 three different kinds of males and females in this species (Benham). 



Mr. A. Treadwell 3 is of opinion that the muscles of the anterior (unmodified) region 

 of such as Nereis hobiensis, Mcintosh, are greatly reduced in the Heteronereis condition, 

 whilst those of the posterior region are not. He also thought that the septa had 

 disappeared. His preparations, however, were imperfectly preserved, so that he speaks 

 with reserve. 



The family of the Nereids is, as Claparede observes, a homogeneous one, and there is 

 little difficulty in assigning the representatives to it. Yet the foreign species are still in 

 want of elucidation, and those from widely divergent regions may yet be brought into 

 closer relationship than is at present possible. 



It is interesting that, as a general rule, the two heterogomph bristles of the upper 

 group in the inferior setigerous process are stouter and often more deeply tinted yellow, 

 just as in certain Syllids. 



The older authors, such as Linnasus, 0. Fabricius, 0. F. Midler, and others, included 

 the Nereids under the Vermes along with parasitic worms, Gordii, Cestodes, Planarians, 

 leeches, Ascidians, parasitic Crustaceans, Echinoderms, and Mollusca. Savigny placed 

 them under his second family of Annelids along with Nephthys, Artcia, Glycera, Oplielia, 

 Hesione, Myriana, Phyllodoce, and Syllis, under the Nereides, whilst the genus Lycoris 

 comprehended the Nereids proper. He was followed by Lamarck, who made the genus 

 Spio an appendix to the former groups. Some of the early authors again confounded 

 the young of the Nereids with Syllids. 



Audouin and Milne Edwards (1834) made them the first genus of their Nereidiens, 

 which included all those treated in this Part. The Nereids were characterized by having 

 the tentacles (the author's antennas) well developed; tentacular cirri on the first segment ; 



1 l Bullet. duMus. d'hisfc. nat.' (C. Gravier), No. 4, 1901. 



3 ' Biological Bulletin/ vol. xix, No. 6, May, 1908, pp. 371—385, with text-figs. 



3 Ibid., vol. ix, No. 4, Sept., 1905, p. 226. 



