STREBLOSPIO. 229 



ment of its pharynx with its two opaque glands posteriorly. The dorsal vessel in the 

 anterior region is very large ; the blood is driven forward by a veritable heart at the 

 limits of the fifth and sixth setigerous segments. Dorsally the larva has reddish-brown 

 pigment; cilia exist on the epaulettes, which support the long bristles of the first 

 segment, on the fifth laterally, and a few on each segment of the posterior region. The 

 digestive tube has, in the posterior region, a border of creamy white. The provisional 

 bristles are not winged, nor crenulate, but absolutely smooth. 



An interesting contribution to the nature of the blood in Magelona was published 

 (1886) by Prof. Benham 1 mainly from observations at St. Andrews. In this the author 

 thinks the blood different from that of any other Chaatopod, and that the rose-coloured 

 globules are non-nucleated, though isolated nuclei occur in the scanty colourless plasma, 

 which is coloured red by haemoglobin. He compares these coloured globules with the 

 coloured plasma of ordinary Chsetopod blood rather than with the coloured corpuscles of 

 the coelom in Capitella, Glycera, and Poly cirrus. 



Ray Lankester 2 (1900), again, considers the condition in Magelona as an advanced 

 case of phleboedesis " which almost extinguishes the ccelomic cavity." 



Hacker 3 (1898) figures (Fig. C) an early stage of Magelona with two long tentacles, 

 and a still longer tuft of swimming bristles, at each side of the head, which remains 

 short. 



The Magelona-l&Yva, described and figured by this author 4 (1898) from the Cape Verde 

 Islands, differs from the ordinary type in regard to the structure of the body and the 

 enlargements of the tentacles, as well as in their great proportional length and structure 

 at that stage. The author rightly calls it a Magelona-like larva, and it is possible that it 

 pertains to another genus of Spionids. 



The able French author, Gravier 5 (1906), describes a species, Magelona obokensis, 

 from the Red Sea, which offers so few differences— the presence of several rows of papillae 

 on the tentacles being one of these— that possibly future observations and the occurrence 

 of intermediate forms may tone down the distinctions, though a papilla above the seventh 

 foot has not been observed in the British form. 6 



Genus CV. — Streblospio, Webster, 1880. 



Prostomium well developed (elliptical or conical) and bearing four eyes. Two ciliated 

 cephalic tentacles. A single pair of large dorsal branchias from the first setigerous segment. 

 Ventral region of the peristomium prolonged forward like a collar. Body cylindrical, of 

 two regions, anterior and posterior, but they are little differentiated. Bristles and ventral 

 hooks from the eighth or ninth segment. No anal cirri. 



The genus Streblospio was established in 1880 by Webster 7 for a small annelid from 



1 ' Quart. Journ. Micr. Sci./ vol. xxxix, n.s., p. 3, pi. i. 



2 'Treatise on Zool./ pt. 2, p. 27. 



3 'Biol. Centralblatt./ Bd. xviii, pp. 41 and 42. 



4 'Plankton Bxped./ p. 20, Taf. ii, figs. 19—20 a. 



5 'Nouv. Archives du Museum/ Paris, t. viii, p. 163, pi. ii, figs. 186—192. 



6 Mr. Southern has found J. P. Moore's Magelona rosea on the west coast of Ireland. 



7 'Rep. Fish and Fisheries, U. S. A./ p. 129, pi. v, figs. 48—50, 1880. 



