-,o6 •ENDEAVOUR" SCIENTIFIC RESl'LTS. 



varies very much in the different specimens examined, for here- 

 there may be either a median paif ol tentacles or a median. 

 U)ipaired one. I ha\e to thank Miss Ethel Summons, Mel- 

 bourne L'niversit\ , for first draw ing mv attention to the paired 

 arrangement. In PI. xxx\ii., figs. 8 to 15, I have represented 

 the bases of the oral cartilages in the mid-\entral portion of 

 the hood of eight different specimens, and it will be seen by 

 them that there is a great amount of variation here. PI. 

 xxx\ii., figs. 8, 9, 10, II, I _' show no median unpaired ten- 

 tacle, but a distinct median pair, while in PI. xxxvii., figs. 13, 

 14, 15 there is a median unpaired one. In I'!, xxxvii., fig. ib. 

 the margin of the oral hood \\ ith the cirri cartilages is repre- 

 sented, and it will be seen that the basal portions of the 

 cartilages of the median pair are smaller than the others and 

 are inclined at a different angle to the margin of the hood, and 

 so are clearly distinguishable. The two ventral cirri repre- 

 sented in PI. xxxvii., fig. 12, are not so clearly paired as in 

 the others. 



In referring to the literature on the subject I can find no- 

 thing very definite. In 1895, Miss J. W. Kirkaldy,^ giving 

 the characteristic features of the Famil} Branchiostomida', 

 says: — "A praeoral muscular hood is developed in front of the 

 mouth, provided along its circular margin with numerous 

 tentacles, supported by a cartilaginoid skeleton ; there is one 

 median unpaired tentacle in the median ventral line, and from 

 ten to twentv (according to age and species) on either side." 



In 187b, Peters^ described Kpliiiniichthys cultcllniu as 

 having ten to twelve pairs of oral cirri, and figuring the under 

 surface of the anterior end draws the cirri showing clearly that 

 there is 110 median cirrus, but he does not state definitely the 

 presence of a median \entral pair. Miss Kirkald}-, howe^ er, 

 in her paper, describes this species as having forty-one to- 

 fortv-three oral cirri, thus gi\'ing it a median tentacle. 



Then, again, Mr. j. D. F. (iilchrist^ gi\ es the number of 

 oral cirri in Branchiostonia capcnsc as thirty-six in all. If, 

 as is generally taken to be the case, the cirri are paired on the 

 two sides of the hood (with the exception of the median ven- 

 tral one), /.('., if the number of cirri is the same on the two 

 sides, this would not allow of a median cirrus being present 

 in this species. It is thus evident there is some uncertainty as 

 to the exact arrangement of the cirri and that a structure 

 previously described as characteristic of the Family Branch- 

 iostomidcC is actuall} subject to variation within the limits ol 

 a single species. 



1 J. W. Kirkaldy- Quart. ,Jotir. Micro. .Sci.. xxxvii. 'n.s.). 1895. p. 309. 



2 Peters— Monat. K. Preuss. Akad.. 1876. 



3 Gilchrist- Marine Investigation in South Africa, ii.. 1904. p. 111. 



