852 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



that time, under the name of Stimpsonia aurantiaca. Mr. A. Agassiz 

 has recently described and illustrated this worm, very fully, under the 

 new name, B. KoicalevsJcii, in the Memoirs of the American Academy 

 of Arts and Sciences, vol. ix, p. 421, and he has also given an account of 

 its remarkable development and metamorphoses, proving that the larva 

 is a free-swimming form, long known as Tornaria, and generally sup- 

 posed to be the larva of a star-fish. This worm, when full grown, attains 

 a length of six inches or more and a diameter of about a quarter of an 

 inch. The body is elongated, tapering gradually, with a loug, slender 

 posterior portion. The body is somewhat flattened dorsally throughout 

 most of its length. At the anterior end it is furnished with a broad 

 thickened collar, in which large numbers of mucus-secreting glands are 

 situated ; the anterior border of the collar is undulated, and from within 

 the concavity, on the dorsal side arises a large muscular proboscis, which 

 has a distinct peduncle, or narrower basal stem, above which it swells 

 out into a somewhat flattened, long, pyriform, or elongated and sub- 

 conical form, the shape constantly changing during life. The proboscis 

 is somewhat wrinkled longitudinally, and more strongly horizontally, 

 being furnished with muscles running in both these directions, and its 

 surface contains mucus-secreting glands. According to Mr. Agassiz 

 the cavity of the proboscis is not connected with the alimentary canal, 

 but opens externally by a pore at the end, and by a narrow slit on the 

 ventral side near the base, in advance of the mouth. The mouth is 

 large and situated at the base of the proboscis on the ventral side. For 

 some distance along each side of the back, behind the collar, is a row 

 of complex gills; these are remarkable on account of their structure 

 and position; they are formed from diverticula of the oesophagus and 

 finally communicate with a row of external orifices situated along each 

 side of the median dorsal-vessel. The gills are supported by a system 

 of solid supports, constituting a sort of internal skeleton; the base of 

 the proboscis is also connected with a firm internal frame-work. The 

 color of this species is somewhat variable ; in young specimens the body 

 was brownish yellow with lighter mottlings, the collar red, aud the pro- 

 boscis white ; in large specimens the proboscis is pale reddish yellow, 

 the collar darker colored, the body purplish or brownish, the sides mot- 

 tled with greenish and whitish, owing to the lateral organs or liver 

 showing through. The proboscis of this worm, according to the obser- 

 vations of Mr. Agassiz, is the principal organ of locomotion, but the 

 collar also aids in the movements. The proboscis appears to be used 

 much as certain bivalve mollusks, such as Solen, Petricola, &c, use their 

 foot in burrowing; the end being contracted to a point, is thrust for- 

 ward into the saud ; water being then forced into it, by the muscles far- 

 ther back, the end expands into a bulb, enlarging the hole and giving a 

 point of resistance toward which the rest of the body can be drawn; 

 the front part of the proboscis being again contracted aud the water 



