210 Mr. F. S. Conant on the Chcetognaths. 



and the other by the absence of those features, is of itself 

 enough to condemn the system. But at the same time it 

 seems to me that Grassi's objections to the system of Langer- 

 hans, as based upon structures of such slight morphological 

 importance as the fins and teeth, are equally sound. Yet 

 the classification of Langerhans is very convenient, and on 

 this account, and because it has been adopted by the last 

 writers on the Chsetognaths, I have followed it, except in one 

 case — in the systematic portion that is appended. But that 

 it, as well as the others, is unsatisfactory, can be readily 

 shown by instances from the American species, in addition to 

 the cases given by Beraneck. 



For example, Spadella schizoptera^ according to Langer- 

 hans and Hertwig, would be called a Sagitta on account of 

 its five fins ; only Grassi's system would retain it with the 

 closely related Spadella cephaloptera. 



Spadella maxima in the classification of Langerhans would 

 belong to the genus Krohnia or to the genus Spadella^ 

 according as the fins or the teeth were accounted the more 

 important ; for its one pair of lateral fins lies partly on the 

 trunk, partly on the caudal segment {Krohnia)^ while the 

 teeth are in two series {Spadella). According to Grassi, it 

 would probably be placed in his genus Spadella {Sagitta of 

 the others), for none of his characteristics for the genus 

 Sagitta {Spadella of the others) was found in the specimens 

 studied. And yet in its coloration and in its habitat near the 

 bottom it is evidently allied, notwithstanding its size, to the 

 small Spadellce. 



By Langerhans Krohnia hamata is set apart with one other 

 species to form a genus by themselves, characterized only by 

 the fact that in connexion with one part of lateral fins there 

 is but one series of teeth. According to Hertwig it is in- 

 cluded with the Sjjadellce^ notwithstanding its free-swimming 

 life at the surface. According to Grassi it would probably be 

 included with the Sagittce (his Spadellce), although the form 

 studied by me showed the transverse musculature that is a 

 characteristic of the Spadellce (his Sagittce) . 



These cases are additional proof that none of the divisions 

 of the Chaitognaths into genera is satisfactory ; while for con- 

 venience' sake and from deference to the later writers I have 

 followed the classification of Langerhans, it would perhaps 

 have been as well to give up the distinctions Spadella and 

 Krohnia altogether, and retain only the one genus Sagitta. 



