222 MAGELONA. 



stances a series of small branches are observed connecting the foregoing artery and vein 

 After the current goes on with rapidity, a large branch suddenly appears nearly opposite 

 the bristle-tuft, and the blood turns backward to the large sacculated chamber. A retro- 

 grade movement next takes place in the anterior part of the vessel, so that the pouch is 

 much distended. Then the chamber just mentioned contracts, driving the blood vigorously 

 forward along the vein into the dorsal trunk. These stages are repeated at short intervals. 

 A large branch of the artery joins the vein above and below the point at which the vessel 

 to the sac comes off, and when the chamber is in process of distension by the backward 

 current both pour their blood into its neck. This arrangement was noticed by Dr. Fritz 

 Midler, and his figure, though incomplete and inverted, is interesting. Further, in each 

 segment small branches proceed from the ventral to the alimentary wall, pass outward 

 over it and then turn upward to join the dorsal trunks. These intestinal vessels branch 

 and communicate with each other. No vessel enters the feet or lateral processes. 



The blood forms a pale rose-pink fluid charged with minute corpuscles, which, after 

 extrusion, group themselves in various masses. The majority of the globules are nearly 

 equal, though there is considerable variety in this respect. They also exhibit molecular 

 motions, and their outline is sometimes altered by pressure. Many are ovoid, some 

 circular or irregularly rounded. If they are examined in the liquor sanguinis, as in a 

 tentacle, many show a shining globule or pale nuclear structure in the centre. Besides 

 the ordinary globules are other bodies, perhaps indicating the development of a globule 

 inside a cell-wall. A minutely granular coagulum is also placed here and there amongst 

 the corpuscles. The blood in the proboscis of a moribund specimen assumes a brownish- 

 red, or by transmitted light a brownish-purple hue. 



The perivisceral chamber can scarcely be said to be functional anteriorly, but behind 

 the ninth segment the body-cavity is considerably altered and enlarged, being rounded in 

 transverse section and containing the alimentary canal, and the dorsal and ventral blood- 

 vessels. The same lining of ccelomic epithelium as in front is present. The chamber is 

 divided into two by the median ligament attached to the blood-vessels dorsally and 

 ventrally. The contained fluid is perfectly translucent, coagulable, and corpusculated. 

 The corpuscles are not very numerous, are circular, oval, fusiform, or irregularly rounded, 

 and besides are flattened. Though some small globules and granules occur, the corpuscles, 

 as a rule, are larger than the blood-corpuscles, with which they cannot be confounded. 

 They show no trace of striae or granulations, only a slight cloudiness in their proto- 

 plasmic centres. In healthy animals they collect in considerable masses in certain parts 

 of the posterior region, and their great size and translucency are striking. The notion 

 that a corpusculated perivisceral fluid and non-corpusculated blood are the rule in the 

 annelids does not hold in Magelo?ia. 



Certain authors— for example, Benham : (1896)— place Magelona under a separate 

 family — Magelonida3, but, so far as observed, it may be retained as a genus of the 

 Spionidse. 



1 c 



Camb. Nat. Hist./ vol. ii, p. 323. 



