36 THE VOYAGE OE H.M.S. CHALLENGER. 



Budding. — The fact that Cephalodiscus is free while Iihahdo2)leura 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 ccenoecium or tubarium) is an important difference. 

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

 •pleuva, the youngest nearest the terminal polypide, the oldest next the distal. The 

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

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

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

 complete development of the i^olypide in Rhahdopleura, there is no evidence that it 

 takes upon itself bud-production ; that is to say, the buds are given ofi" 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 Rliahdo2^leura, 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 Cejyhcdodiscus. The source of 

 the hypoblastic elements, if these are present, in the bud of Rhahdopleura is thus in 

 obscurity. In PJioronis no bud 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 (Tornaria). 



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 Ceplialo- 

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

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

 phora of Professor AUman. 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 ccenoecium, its digestive 

 system, and its buds, and it is peculiar 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 ccenoecium of Rhahdojjleura or Cephalodiscus is constructed. While again the 

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

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



