240 THE GREAT BARRIER REEF. 



E. A. Minchin, who has recently investigated the phenomenon as exhibited by this species — 

 {Annals and Magazine of Natural History, October, 1892, p. 273) — has found that the organs 

 normally attached to the external wall of the intestine when first discharged pierce the walls 

 of the cloaca, and are then shot out through the rectum after the manner of a rocket. Each 

 individual organ or filament, when first released, possesses an inflated head, which becomes 

 gradually diminished in size as the thread elongates, and until it reaches, so to say, the ex- 

 treme length of its tether. The actual or determining cause of the lengthening process remains, 

 as yet, undiscovered — an inherent automatic power of elongation — the unreeling of an 

 enclosed spiral thread — the action of water pressure forced in from the cloaca, — have been 

 respectively advocated by authorities as furnishing a probably correct interpretation. Having 

 regard to the extreme tenacit}' and plasticity of the Cuvierian filaments, and their develop- 

 ment in manj- of the Great Barrier species in such copious masses, the suggestion arises 

 whether the substance could not be turned to economic use as a substitute for caoutchouc. Its 

 tenacious, glue-like consistence, when first extended, and its flexible and elastic properties when 

 subsequently dried, appear to lend some support to the anticipation of latent possibilities in this 

 direction. 



In the coloured plate, Chromo XII., illustrating various representatives of the Beche-de-mer 

 tribe, there are one or two figures which would appear at first sight to possess no legitimate 

 claim for admission among this class of organisms. The first of these. Fig 3A, is a species of 

 flat, large-scaled worm, closely allied to the familiar Polynoc sctosa of European seas ; but, in place 

 of lurking under stones on the seashore, as does that species, this form is invariably associated 

 with the bottle-green-tinted Beche-de-mer, Sticliopiis cliloronottts, figured immediately beneath it. 

 Clinging closely to the integument of the Holothurian, in the interspaces betwixt the projecting 

 papillae, it can, in life, be scarcely detected, the colours in the two animals perfectly harmonising. 

 By way of comp"arison with the ordinary representatives of the genus Polynoe, the parapodial 

 appendages of this commensal type are specially modified to the form suckers which enable 

 it to cling to its elected host. A corresponding commensal annelid has been found by the 

 author associated with the species of Beche-de-mer, Actinopyga ntauritiaiia, previously described 

 under the title of Surf-red. In this instance it has also adapted itself to the colour of its host, 

 being of a clear red-brown hue. There are some species of Beche-de-mer that entertain guests 

 on much more intimate terms than those of mere outside "hangers-on," such as are these 

 annelids. The fish, for example (a species of Fierasfer), delineated in Fig. 10 of Chromo XII. 

 — inhabits the body cavity of the large teat-fish, Holothuria mammifera, in the same manner 

 as the two species of Amphiprion (figured in Chromos I. and II.) lodge with their associated 

 anemones. Among the Beche-de-mer fishers, these commensal fish are popularly known by the 

 name of " Glass Eels." So far as the author has been able to ascertain, the above-named 

 species of Holothuria is the only one among the many known varieties that shelters a Fierasfer. 



