6 THE VOYAGE OF H.M.S. CHALLENGER. 



adherent. In no case, however, do these form a regular layer. The tenacity of this 

 secretion is considerable : thus, when a young example is attached to the tube of an 

 adult, it is almost impossible to remove it without rupture of the contained animal. 



The habit of this species, therefore, differs considerably from the Australian form 

 described by Dr. Haswell, which seems, in vast numbers, to find sufiicient protection in 

 the thick semi-gelatinous case or tube of Cerianthus, composed as it is almost entirely 

 of the large ovoid thread-cells of the Actinia — the threads in most cases having 

 escaped, though a few are still in the interior of the cysts. The only other constituents 

 of this remarkalile Ijlackish felt are a few sponge-spicules and grains of muddy sand. 



Tubes have been found in almost all the species of Phoronis hitherto described, 

 the hypodermic secretion being mingled with mud or sand. Schneider makes the 

 curious statement, that the tube in his form had in it Fungi and Infusoria. No author 

 seems to have connected the presence of these tubes in holes in limestone and other 

 rocks, and in shells with the power of perforation ; but it seems to me that in future 

 this genus will in aU probability have to be included in this interesting group. 



External Form. 



The total length of Phoronis hushii (PL I. fig. 1) is about 52 mm., with a variable 

 diameter of about 2 mm. at the blackish anterior region, and 4 or 5 mm. at the 

 enlarged posterior part. The tentacular or branchial region has a length of 6 or 7 mm. 

 The species thus exceeds in size any hitherto described, and is even considerably longer 

 and more bulky than the Australian form. Observers, as a rule, have worked with 

 specimens — like those of Kowalewsky's at Naples — measuring about 14 lines in length. 



The body (PI. I. fig. 1) is elongate, smoothly rounded to the naked eye, and 

 generally thrown into several constrictions and enlargements, as in Phascolosoma, or in 

 certain examples of Cerianthus and Edivardsia, the bulbous posterior end (devoid of 

 all transverse wrinkles) of many making the resemblance to the latter all the more 

 striking. On the other hand, the double branchial fan and general appearance approach 

 the contour of the Eriographididas and Sabellidse amongst the Annelids. The anterior 

 third of the body, which is tinted of a blackish hue (it may be somewhat purplish 

 during life), with a slight metallic lustre — fading posteriorly, is most minutely marked by 

 fine transverse lines — as in the massive muscular proboscis of Lejndonotus and Aphro- 

 dita. These circular striae are much finer in front, and gradually widen towards the 

 posterior part of the coloured or anterior region, which in almost all the specimens is 

 firmly contracted, from the peculiar structure of the body-wall. The dorsal (PL I. fig. 1) 

 is distinguished from the ventral surface (PL I. fig. 2) by a longitudinal furrow — on each 

 side of the median line — cutting ofi" a ridge or fold, underneath which the rectum passes. 

 This feature was formerly noticed in the smaller specimens by Schneider. In many 

 the body gradually dilates toward the end of the anterior region, and an enlarged pale 



