1 DISTRIBUTION COLOUR HABITS 7 



depth of about eight inches. The greater part of the body is 

 coiled in an even, cork-screw-like spiral, while the anterior end, 

 including the front part of the branchial region, is maintained 

 in a vertical position. The posterior end is also kept upright, 

 and can be moved up and down in a vertical shaft opening on 

 the surface, thus enabling the animal to eject the undigested 

 sand from its anus. 



The coloration of Balanoglossus is often brilliant. That of 

 D. koivalevskii ^ is as follows : — The " proboscis " (cf. Fig. 1, B, ^) 

 is yellowish white ; the " collar " (c) is brilliant red-orange 

 (especially in males), with a white ring posteriorly ; the " trunk " 

 (f), the subdivision of which into " branchial," " genital," " hepatic," 

 " abdominal," and " caudal " regions is better indicated in other 

 species (Fig. 1, A, b, g, h, ab), is orange-yellow, shading to green- 

 yellow in the semi-transparent caudal region. The genital region 

 is grey in females and yellow in males, a sexual difference in 

 colour being common in Enteropneusta. The hepatic papillae of 

 other species may be bright green. 



The odour of I), kowalevskii resembles that of " chloride of lime 

 with a faecal admixture," while that of Balanoglossus aurantiacus 

 suggests iodoform. All Enteropneusta are said to have a more 

 or less offensive smell. A species of Balanoglossus is known to 

 be intensely phosphorescent.^ 



The mouth (Fig. 7, m) is situated on the ventral side, at the 

 base of the proboscis, and is concealed by the free anterior edge of 

 the collar, which encircles the thin "proboscis-stalk" (Fig. 3,|?.s). 

 The animal has the singular peculiarity of being unable to close 

 its mouth ; ^ and thus, as it burrows through the ground, the 

 sand which passes into the alimentary canal leaves it in a 

 continuous column through the terminal anus."* The large coiled 

 "castings" formed in this way between tide-marks enable the 

 experienced collector to infer the presence of Balanoglossus ; and 

 in a West Indian species described by Willey ^ they are so large 

 as to form " an important feature in the landscape at low tide." 



The principal agents in burrowing are the proboscis and collar. 

 An animal observed by Spengel pushed the tip of its proboscis 

 into the sand, waves of muscular contraction meanwhile passing 



1 Quart. J. Micr. Sci. xxv. Stipiil. 1885, p. 91. 



3 Pouohet, C. R. Ac. Sci. cii. 1886, p. 272. 



3 Kowalevsky, Mim. Ac. St. Petersh. (7) x. No. 3, 1866, p. 7. 



" Spengel, Momgr. p. 474. '■ Zool. Res. Pt. iii. 1899, p. 256. 



