S6 THE TOYAGE OF H.M.S. CHALLENGER. 



Budding. — The fact that Cephalodiscus is free while Rhabdopleura is fixed causes 

 considerable divergence in regard to the buds ; and, moreover, the functions performed 

 by the bud in- the latter species, while yet incompletely developed, and with a bifid 

 buccal shield (viz., the secretion of the coencecium or tubarium) is an important difference. 

 Another essential divergence is the occurrence of the buds in a regular series on Rhabdo- 

 pleura, the youngest nearest the terminal polypide, the oldest next the distal. The 

 confinement of the buds in Cephalodiscus to the region just within the terminal 

 hypodermic plate is peculiar, and makes it difiicult to institute anything like parallelism 

 between them in this respect. Further, Lankester is inclined to think that after the 

 complete development of the polypide in Rhabdopleura, there is no evidence that it 

 takes upon itself bud-production ; that is to say, the buds are given off at an early period 

 of its growth. It is not quite clear, however, that the budding of this form is in the 

 same category as that of Cephalodiscus, in which the stalk is a process of the body-cavity, 

 whereas the soft stalk of Rhabdopleura, if the descriptions are understood correctly, has 

 not yet been shown to be so, though at first sight it might be interpreted otherwise. 

 Nothing like the arrested buds of this form is known in Cephalodiscus. The source of 

 the h}rpoblastic elements, if these are pr-esent, in the bud of Rhabdopleura is thus in 

 obscurity. In Phoronis no biid- is known, while the small ova are extremely numerous, 

 and the embryos (having the form of the well known Actinotrocha) pelagic. In 

 Balanoglossus likewise no bud occurs, the ova are numerous and small, and the embryo 

 free-swimming (Toruaria). 



On taking a general survey of the subject, then, it occurs to me that in the present 

 state of our knowledge, and while fully admitting the remarkable resemblances between 

 it and certain hitherto isolated types such as Balanoglossus (which I have for the most 

 part left in the able hands of Mr. Harmer), it will lead to no disadvantage if Cephalo- 

 discus be left as formerly near the Polyzoa ; and, further, though the divergences between 

 it and Rhabdopleura are noteworthy, in the same group as formerly, viz., the Aspido- 

 phora of Professor AUmau. It is well to exhaust the structural, developmental, and 

 other features in the various forms reviewed in the preceding paragraphs before changes 

 in classification are promulgated. 



Cephalodiscus approaches the Polyzoa in regard to its coencecium, its digestive 

 system, and its buds, and it is pecuhar that in these points there is a lack of conformity 

 in Balanoglossus, and to some extent in Phoronis. Viewed as a whole, the several 

 systems mentioned agree most with the type of the Polyzoa. Though Phoronis forms a 

 tube, and Balanoglossus secretes very abundant mucus, a feature common to many 

 diverse groups, such as the Nemerteans, Discophora, and MoUusca, nothing like the 

 regular coenoecium of Rhabdopleura or Cephalodiscus is constructed. While again the 

 digestive system of Phoronis resembles that in the Polyzoa, the same system in Bcdano- 

 glossus is very diff'erent, for the straight alimentary canal with its terminal anus has no 



