THE HYDROIDS OF THE SCOTTISH NATIONAL ANTARCTIC EXPEDITION. 



85 



(Marktanner-Turneretscher (1890) gives the variation as from three to ten pairs 

 per internode.) 



The hydrothecse are almost wholly immersed, and the " free membranaceous extension 

 of the wall," too prominently figured in Allman's account, has been destroyed (as indeed it 

 was in the T. pectinata specimen examined), leaving a jagged edge level with the general 

 outline of the pinna. There is evident on the abcauline wall of the hydrothecse, just 

 within the opening, a small knob of chitin, and immediately above or upon this rests the 



PlG. 6.— Thuiaria articulata. (a) Single internode of stem with proximal internodes of pinnae, x 20. (b) Gonangium. 

 x 12. (c) Internode from T. pectinata with hydrothecse slightly apart, x 20. {d) Internode from T. pectinata with 

 congested hydrothecse. x 20. 



base of the one-flapped operculum. On the stem internodes and on the younger pinnae 

 the hydrothecae are slightly apart from each other, but in the older pinnse they are 

 compressed and lie closely packed, the distal end of one forced against the base of its 

 successor (cf. fig. 6, c and d). 



The gonangia are clustered on one face of the stem and on the corresponding 

 faces of the pinnse. They arise immediately beneath a hydrotheca, are elono-ate 

 oval in shape, with a wide, circular, distal opening bordered by a distinct neck, 

 and with a tapering proximal end. Their distal half bears more or less indefinite 

 annular rugosities. 



