CHAETOGNATHA. 



WITH A NOTE ON THOSE COLLECTED BY H.M.S. 'CHALLENGER' IN 

 SUBANTARCTIC AND ANTARCTIC WATERS. 



By G. Heebert Fowler, B.A., Ph.D., F.L.S. 



(1 Chart.) 



I.— THE COLLECTION OF THE 'DISCOVERY.' 



The specimens mentioned below include all those taken south of 40° S., a parallel 

 selected to include what appear to be the critical temperatures which separate a 

 temperate and subantarctic plankton from truly Antarctic forms. The material was 

 preserved in alcohol, and was mostly in fair condition, but presented the usual 

 disadvantages which attend upon the use of this reagent for Chaetognatha. 



Only three species were represented. The tables of formulae,* giv^en under each 

 species, serve to show the relation between the more obvious variations which occur in 

 these southern specimens and those in specimens from other localities. In these tables 

 the first column of figures gives the total length in millimetres (including the tail fin) ; 

 the second, the length of the tail expressed as a percentage of the total length ; the 

 third, the number of jaws ; the fourth, the number of anterior teeth (or of the only row 

 of teeth in the ease of Krohnia) ; the fifth (when present), the number of posterior 

 teeth. 



Sagitta hexaptera. 



Sajitta hexa^Jtera, D'Orbigny, Voyage dans TAmerique meridionale. Tome V., 3"°" partie ; Mollusques, 

 p. 143. (1835-1843.) 



The species was represented by numerous specimens. They agreed with typical 

 hexaptera in almost every one of such diagnostic features as they had retained, the 

 exceptions being that the anterior fin appeared to extend slightly further forward than 

 is usually the case (due possibly to imperfect preservation), and that the first (newest) 

 jaw hardly showed the usual ridge and bay just below the tip ; the extent to which 



* The latest papers on Chaetognatha, summarising the distribution and literature of the group, are : " Biscayan 

 Plankton collected during a cruise of H.M.S ' Research,' 1900, Part HI. — The Chaetognatha " ; Transactions of 

 the Linnisan Society, 2nd Series, Zool., Vol. X., pp. 55-87; and " Reports of the ' Siboga' Expedition. Mono- 

 graph XXr., The Chaetognatha" (Leiden, 1906). 



VOL. III. Y 



