﻿004 •ENDEAVOUR" SCIENTIFIC EESULTS. 



other tentacles. As regards this point, W'illeyi writes: — "It 

 is important to note that the buccal skeleton grows at each 

 end only, and that fresh elements are not formed interstitially. 

 In the adult the median cirri are smaller than the others ; and 

 one would at first naturally suppose that these were the 

 Youngest, and that this was the point at which fresh cirri 

 would be ft)rmed ; as a matter of fact, however, the small size 

 of the median ventral cirri of the adult is deceptive, for they 

 are the oldest cirri, and new ones are only added at the free 

 extremities, right and left, of the buccal skeleton." Therefore 

 I think the hoods with the tentacles arranged as in PI. xxxvii., 

 figs. 6 and 7, are also of the ordinary type, having a median 

 unpaired tentacle. 



The oral sphincter is situated in a line with the angle of the 

 sixth myotome, and has about fifteen velar tentacles. 



The ventral fin has chambers and fin rays. I have not been 

 able to determine whether the rays are single or double. 



The dorsal fin is about one-thirteenth the vertical height of 

 the body, and the fin rays stop behind about the 49th myotome. 



The riglit metapleur is continuous behind with the median 

 ventral fin, the left stops immediately behind the atriopore. 

 There are two post-atrioporal ca'ca, the right continuing 

 much further back than the left and reaching almost to the 

 anus. 



The i^onads are arranged in a single series on the right side 

 and varv in number from 17-22. An important point noted 

 is the presence of the gastrula stage of the egg. In examining 

 the specimens I found several of the ova in this stage, but 

 thev are not preserved well enough for a good microscopical 

 examination. 



The above characters would place the species in the same 

 subdivision of the genus Asynimetynn as that in which we pre- 

 viously placed A. hassanum.^ 



In length, number of myotomes and myotome formula, and 

 the number of oral cirri, Asymmetron anstralis agrees very 

 closelv with Heteropleiiron hedleyi, found in Torres Strait, 

 and described b^ Professor W. A. Haswell.'^ The rostral fin, 

 however, differs in being raised above the level of the dorsal 

 fin and in being more expanded ; the dorsal fin rays extend 

 further back, and ventral fin rays are present. In the descrip- 

 tion of H. Jiedleyi there is no mention of the post-atrioporal 

 region of the atrial cavity, nor of the oral hood excepting the 

 number of oral" cirri. 



1 Willey -Quart. Jour. Micro. Sci., xxxii., 1891, p. 214. 



2 Morris & Raff — Notes on the Structure of Asymmetron ho usa num— Ft oc. 



Roy. Soc. Vict., xxii. fn.s.), Pt. I., 1909, p. 88. 



3 Haswell— Rec. Austr. Mus., vii., 1, 1908, p. 33, fig. 1. 



