SPIONHLE. 137 



anterior and posterior dorsal bristles are generally capillary, and the anterior shorter 

 and larger than the posterior and often punctated. These bristles become very fine 

 posteriorly and in certain genera (e.g. Pygospio and Poly dor a) disappear more or less 

 completely. The posterior dorsal bristles in Marenzelleria, JSTerine, and Aonides are winged 

 hooks, and in Magelona the same occurs after the tenth. The anterior ventral are shorter 

 than the posterior, large and generally punctated. The inferior ventral are generally 

 winged and often punctated. The bristles may be shed and renewed, hence various 

 differences. The bundles of fine bristles enclosed in the tissues he and Griard consider 

 defensive, and may be ejected. Mesnil compares these with the bacilliporous corpuscles 

 in Polydora fiava. As a rule the Spionids have no extrusible pharynx except in 

 Magelona, but this statement seems to need revision. The blood-vascular system is well- 

 developed, but contains no corpuscles except in Magelona. In each segment a vascular 

 ring connects the dorsal and ventral trunks. These branches send vessels to the 

 branchiae. Except in Magelona a single blood-vessel only occurs in the tentacles. The 

 branchiae are always simple and richly ciliated, and a dorsal ciliated band connects 

 them across the body, and this is specially developed in Spiophanes where no branchiae 

 are present. 



The larvae of Spionids are widely distributed throughout the ocean, and numerous 

 forms were found in the " Plankton Expedition " and described by Hacker 1 (1898). Some 

 of these so closely resemble the larvae of British species that they probably belong to the 

 same genera, e.g. the Polydora larvae. So far as can be judged the authors' Ghsetosphmm 

 larvae do not belong to ordinary Spionids, but in Fig. D somewhat approach Pdecilo- 

 chsetus. 



In the Spionidae, Goodrich 2 (1900) notes that the nephridia open internally, and that 

 the genital funnel becomes connected with the nephrostome and loses its primitive opening 

 to the exterior. 



Salensky 3 (1908) has made important observations on the structure and development 

 of the pharyngeal pouches of Polydora and Scolecolepis fuliginosus. In the former they 

 are two in number, the anterior passing directly forward from the mouth, the posterior 

 sloping obliquely forward and outward at its sides. In Scolecolepis fuliginosus these 

 pouches, likewise occur in similar positions, though somewhat modified. The author 

 compares these with what he found in Polygordius and Saccocirrus, and comes to the 

 conclusion that these fissures or pouches are indications of the gill-clefts in the Chordata 

 and Enteropneusta. 



Viguier 4 (1910) described an interesting case of precocious maturity in larval 

 Spionids (Nectosoma), 1*6 to 1*8 mm. in length, in which both males and females occurred. 

 He thinks they are apparently larvae of a sedentary form which has become paedogenetic 

 and pelagic. Viguier' s larvae somewhat resemble Graveley's (Plate XIV, fig. 5), and the 

 males have eight segments besides the head and the pygidium, the females a segment 



1 ' Plankton Exped./ p. 17, Taf. ii, figs. 14 — 18, text-fig. B, and Chsetosplidera, figs. C and D. 



2 ' Quart. Journ. Micr. Sci./ vol. xliii, N.S., p. 740. 



3 'Bull. Acad. Imp. Sc. St. Petersburg/ p. 687, with 23 text-figures. 



4 'Compt. Kend. Acad. Sc./ cli, pp. 104—6; and also (1911) 'Ann. Sc. nat./ 9 e ser., t. xiii, p. 235, 

 pi. viii, figs. 13—17, and pi. ix, figs. 23—30. 



141 



