270 PR J. H. ASHWORTH AND DR JAMES RITCHIE ON THE 



development of the male and female sporosacs, as far as it was traced, agrees with 

 that of our Neapolitan sporosacs. The female sporosac of H. conybearei bears a 

 single oocyte. According to the accounts of Allman and Weismann, the develop- 

 ment of the sporosacs in 17. conybearei stops a long way short of the stage reached 

 by our Neapolitan sporosacs, for in the former no free-swimming stage was observed 

 and no trace of tentacle detected, so that the sporosac was considered by both 

 authors to belong to the fixed type. 



Evidence we have accumulated indicates that the sporosacs of Heterocordyle 

 conybearei examined by Allman and Weismann were not fully mature, and that 

 consequently these authors (whose accounts have been followed by later writers) were 

 misled as to the final structure and essential nature of the sporosacs. The identity 

 of the early stages of the sporosacs of H. conybearei with those of our material has 

 already been pointed out, but it was desirable to ascertain definitely whether or not 

 the later phases were identical, which could only be determined by examining a well- 

 preserved, mature colony indubitably belonging to H. conybearei, and preferably 

 obtained from some source other than Naples. We were unable to obtain such a colony 

 until this paper was standing in proof, when Mr E. T. Browne kindly lent to us a 

 colony, collected near Plymouth in 1895, and identified by him as H. conybearei* — 

 an identification with which we fully agree. This colony covers an area of about 

 9x4 mm. on a portion of a shell, and is probably younger than those from Naples 

 examined by us, since nearly all the stems bear a single hydranth, only a few having 

 two. The characters of the trophosome of Mr Browne's colony are in agreement with 

 those of our Neapolitan examples, but the largest polyps of his colony are distinctly 

 larger than any of ours. Further, the mature blastostyles of his colony are longer 

 than ours (his longest being about 1*3 mm. and ours 7 mm. in length respectively), 

 but have approximately the same width. We do not attach any significance to these 

 differences, as they may both be due to the exceptional conditions under which the 

 Neapolitan examples passed their last days in the seat ( see P- 258). 



The blastostyles of Mr Browne's colony are, with one exception, confined to the 

 stolon, and are for the most part young, only five bearing sporosacs. One blasto- 

 style, which was removed for detailed examination, bears a dozen large sporosacs — 

 evidently its first series — in a cluster slightly distal to its middle. More distal, and 

 extending to the base of the hypostomal area, is a broad zone the ectoderm of which 

 exhibits numerous small elevations (incipient sporosacs) each containing a single 

 oocyte. Had these sporosacs become mature, the blastostyle would have been similar 

 (except in length) to that shown in fig. 1, B iv. The large sporosacs on this blasto- 

 style are about "13 mm. long and "1 mm. broad; each has a single tentacle and a 



" Recorded from Plymouth on shells of Nassa (cf. p. 258) and Buccinum, particularly the former. See Journ. 

 Murine Biol. Assoc, vol. vii (N.S.), p. 190, 1904. 



t It is possible that the Neapolitan and British specimens belong to distinct geographical sub-species or races, but 

 this can only be determined by examination of a longer series of mature examples. 



