NOTES ON THE IDENTIFICATION OF THE 

 CH/ETOGNATHA. 



E. LE ROY MICHAEL. 



Introductory Remarks. 



It is the testimony of all, who have attempted the identifica- 

 tion of the Chsetognatha, that, for so small a group, they offer 

 an immense amount of difficulty. The several species are very 

 similar in appearance so that one is compelled to seek among 

 details of structure for valid taxonomic characters. There is, 

 moreover, considerable variation in most of the characters ; some 

 of the valuable diagnostic features are readily destroyed even 

 with the best possible preservation, and the methods of micro- 

 scopical technique, usually so efficient, fail, for the most part, 

 with the Chaetognatha. It is not surprising then, that, without 

 most careful examination, it becomes easy to base identifications 

 on abnormalities or upon too variable characters. This has been 

 repeatedly done by the earlier investigators with the result that 

 the various species have become so entangled in the literature 

 that, for anyone not a specialist on the group, identification is 

 well nigh an impossible task. To meet this need for an ade- 

 quate and ready means of identification the keys and tables herein 

 presented have been prepared. 



Except in the papers of Fowler ('05, '06), Hertwig ('80), and 

 Krumbach ('03) identification has been based upon characters 

 having little or no taxonomic value. Hertwig's investigations are 

 clear and to the point but, unfortunately, only a few species came 

 under his observations. Krumbach has accurately made a detailed 

 study of the seizing jaws and has developed a classification based 

 upon the minute anatomy of these structures. It is an exceed- 

 ingly valuable contribution for, in many cases of poor preserva- 

 tion, these hard structures offer the only means of identification. 

 There is, however, one difficulty with the Krumbach system : it 

 requires so minute an examination that it is only after one has 

 worked at it for some time that he is able to see the distinctive 



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