358 K. T. GUNTHKR. 



been accumulated. Several of our predecessors liavc already 

 published sucli historical resumes, and so it will suffice to 

 refer the reader to the works of Hertwig, Langerhaus^ aud 

 Grassi for fuller details than we give here. 



In his original description Martin Slabber (1775) expressed 

 the opinion that the " arrow-shaped worms " should consti- 

 tute a sub-division of the Linnean group of Vermes. Quoy 

 and Gaimard (1827), after examining the large Sagitta 

 bipunctata from (libraltar, were uncertain as to whether 

 it was Zoophyte or Mollusc. D'Orbigny (1834), however, 

 decided in favour of the Mollusca, and associated the arrow- 

 worms with the Heteropoda, an association in which he was 

 followed by Milne-Edwards (1845), Troschel (1845), Siebold 

 (1848), and Burmeister (1856). Milne-Edwards, indeed, 

 went so far as to point out that the "prepuce'^ together 

 with the head of Sagitta were the equivalents of the Mol- 

 luscan head. 



The anatomical work of Krohu (1844) marks a new epoch. 

 Having been fortunate in obtaining specimens of large size 

 at Messina, Krohn was able to investigate many hitherto 

 undiscovered details of the internal organisation, and 

 amongst others the nervous system, testes, and buccal 

 apparatus. The result was an alliance of the Arrow-worms 

 with the Annelida. Five years later Oersted (1849) sug- 

 gested that Sagitta should rather be considered as a Nema- 

 tode, an association favoured by Leuckart (1854) and by 

 several writers of zoological text-books (e.g. Glaus). The 

 comparison rests principally upon a certain similarity of 

 arrangement of the musculature. 



Passing over a suggestion of relationship Avith the Tardi- 

 grada and lower Arthropods by Huxley (1852 and 1878), 

 which has been reconsidered by Grassi (1883) on account of 

 fancied resemblances between the cerebral ganglia, we come 

 to the more serious proposal that a new subdivision of the 

 worms should be constituted for the reception of the Sagittre; 

 and of the names proposed, that of Leuckart (1854) — Chaeto- 

 gnatha — has taken precedence of Oesthelminthes of 



