1895. RESULTS OF ''CHALLENGER" EXPEDITION. 65 



number of the species brought home are positively known to occur in 

 the upper Tertiaries, and none of the abyssal forms have yet been 



found in the fossil condition. 



F. A. B. 

 Bryozoa. 



The reports by Messrs. Geo. Busk and A. W. Waters added 

 largely to our knowledge of the variety of form in this group, and 

 acquainted us with the delicate and flexible deep-sea species, though 

 only one could be regarded as belonging to a decidedly abyssal family 

 — the Bifaxariadae. The geographical distribution of the abyssal forms 

 bears no evident relation to the bathymetrical. Still less is light 

 thrown on the fossil species. In fact the chief interest possessed by 

 the Bryozoa of the " Challenger" has now been removed from them 

 by the transference of Cephalodiscns to the group next considered. 



Hemichordata. 



Cephalodiscus may fairly claim to be one of the most novel types 

 which have been made known as the result of the voyage of the 

 " Challenger." This extraordinary animal was dredged in the Straits 

 of Magellan, at a depth of 245 fathoms. No special attention seems 

 to have been paid to it on that occasion, and the first cursory 

 examinations which were afterwards made gave no clue to its real 

 affinities. 



The animal (PL xv., Fig. 5) measures some 2 mm. in length, and 

 is provided at its anterior end with six pairs of multipinnate ten- 

 tacular arms. Near the other end the body is produced into a short 

 stalk, from the tip of which buds are produced. These buds break 

 off after reaching a certain stage of development, so that no "colony," 

 in the ordinary zoological use of the term, is produced. The 

 animal is, however, gregarious, and large numbers are found in the 

 cavities of a semi-gelatinous " coenoecium," which is the product of 

 their joint activity. The analogy of Rhabdopleiira suggested that the 

 coenoecium was in large part at least secreted by the " buccal shield" 

 or proboscis. 



Although the affinity of Cephalodiscus to Rhahdoplnira was soon 

 recognised, it was first shown in the " Challenger " Report that the 

 former animal was unmistakably allied to Balanoglossus. No con- 

 clusion could have been more unexpected. The two genera are 

 totally unlike at first sight ; their internal structure is identical in 

 all essential particulars. 



The three main regions of Balanoglossus, the proboscis, the collar, 

 and the body proper, are clearly marked in the immature buds (Fig. 

 8) of Cephalodiscus. The divisions of the body-cavity corresponding 

 to these regions are distinct and separate even in the adult animal ; 

 and consist, as in Balanoglossus, of an unpaired proboscis-cavity (b.c.^), 

 and of paired cavities (b.c.-, b.c.^) belonging to the two succeeding 

 regions. Two of the special peculiarities of Cephalodiscus are the 



