X 



OBSERVATIONS ON THE GENUS SAGITTA. 

 British Association Report, 1851, pt. ii. pp. 77-78 {Sectional Transactions). 



Mr. Huxley made some observations upon the structure of the 

 anomalous genus Sagitta, which has already been more than once 

 a subject of discussion at the Meetings of the British Association. 

 Mr. Huxley's statements essentially confirmed those of M. Krohn ; 

 the existence of a ciliated canal or oviduct in the outer part of the 

 ovary being the only new fact of any importance brought forward. 

 The very wide geographical distribution of Sagitta was alluded to, 

 the animal having been found in all the seas through which H.M.S. 

 Rattlesnake passed in her circumnavigatory voyage. 



In discussing the zoological relations of Sagitta, Mr. Huxley's 

 remarks were to the following effect : — Sagitta has been placed by some 

 naturalists among the MoUusca, a view based upon certain apparent 

 resemblances with the Heteropoda. These however are superficial ; 

 the buccal armature of Sagitta, for instance, is a widely different 

 structure from the tongue of Firola, to which, when exserted, it may 

 have a distant resemblance ; the distinct striation of the muscular 

 fibre, and the nature of the nervous system, equally separate Sagitta 

 from the Mollusca. 



There appears to be much more reason for placing this creature, as 

 Krohn, Grube, and others have already done, upon the annulose side 

 of the animal kingdom, but it is very difficult to say in what division 

 of that sub-kingdom it may most naturally be arranged. At first 

 sight it seems to present equally strong affinities with four principal 

 groups, viz, — I. the Nematoid worms; 2. the Annelida; 3. the 

 Lernsean Crustacea ; and 4. the Arachnida. 



I. With the Nematoid worms it is allied by its general shape and 

 habit, its want of distinct annulation, and remotely, by the armature 



