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



He considers Phoronis a true Gephyrean, and that the flexure of the alimentary canal 

 (which resembles that habitually assumed by Sahellaria) is the result of the coalescence 

 of the parts— of a primitively straight form— thus approximated by the exigencies of 

 its life. Further, he explains how this metamorphosis came to be carried out abruptly, 

 mainly from its great advantages to the form. 



In the same year a preliminary account of the large species procured by the 

 Challenger was communicated by the author to the Eoyal Society of Edinburgh.^ 



Dr. Haswell next noted " the occurrence of a closely allied form, somewhat less in 

 size, inhabiting the semi-sjelatiuous investment of the remarkable Actinia — Ceriantlms. 

 In his own words, " The present species, which I propose to name Phoronis australis, 

 was obtained on two occasions during the dredging work carried on under the auspices of 

 the Trustees of the Australian Museum, at a depth of fifteen fathoms, off" Ball's Head, 

 in Port Jackson. ... A number of individuals inhabit a large irregular semi-gelatinous 

 sac, about six inches long and three or four wide, and open at both ends. The walls of 

 the sac, which range from | to | an inch in thickness, and are tolerably tough, are 

 composed of numerous fine threads closely felted together, and in these walls, in wide 

 irregular species among the felted threads, lie the worms, the head projecting externally; 

 the inner surface of the sac is lined by a dense glistening layer of the same material as 

 the rest. The whole substance of the sac is of a purple colour." This description was 

 drawn up before the identity of the tube was recognised, but Dr. Haswell afterwards 

 found Ceriantlms inside, and was good enough to forward several examples to me. He 

 has also subsequently mentioned that the larval forms (Actinotrocha) are obtained by 

 the tow-net on the surface throughout the greater part of the year. 



The following year (1883) Mr. Caldwell presented a preliminary note on the 

 structure, development, and affinities of Phoronis to the Royal Society.^ This is an 

 able and comprehensive contribution on the subject, the observations and conclusions 

 arrived at by the author being noticed under the several heads in the body of this paper. 

 In his remarks on the metamorphoses of some Bryozoa, Dr. Jules Barrois* 

 especially refers to the comparison instituted by Sydney Harmer and Ostrooumoff' 

 between the evagination of the internal sac of the Bryozoa and the ventral tube of 

 Actinotrocha. Ostrooumoff groups the Bryozoa into three great types: (l) in which 

 the skin of the adult is formed mainly by the evaginated sac {e.g. Phoronis) ; (2) in 

 which the skin is formed by the aboral face enveloping the rest ( Vcsieularia) ; and (3) 

 in which the skin is formed in part by both faces (Chilostomata). Barrois himself 

 reduces them to two great types, viz. (l) those characterised by the predominance of 

 the ventral face, and the reduction of the dorsal to the terminal region of the body ; 

 and (2) those distinguished by the predominance of the aboral face (the cephalic of the 

 trochosphere) which envelopes the oral (somatic). 



1 Proc. Roy. Soc. Edin., vol. xi. pp. 211-217, 1880-82. « p^o,-. Unv. Soc. N.S.W., vol. vii. p. 606. 



8 Proc. Roy. Soc, vol. xxxiv. pp. 371-383. ■• Ann. d. Sci. Nal., t. i. pp. 83-86, 1886. 



