M. T. Thorell on the Arrangement of the Copepoda. 447 



are attacked by A. foliaceus, one by A. catostomi. Cyprinodonta 

 have afforded A. funduli ; the Characinidse A. Nattereri, A. sal- 

 mini and G. longicauda. Salmonoids are affected by A. coreyoni 

 and A. foliaceus, which has also been taken on an Esocoid ; the 

 Clupeidse finally have contributed a species, A. alosa. Among 

 the Pharyngognathi the family Chromidse has a parasite in A. 

 ehromidis ; and among the Acanthopteri it is the families Scom- 

 bridse (for A. purpureus and foliaceus), Sparidse (for A. pur- 

 pureus), and Percidse (for A. foliaceus) on which representatives 

 of the Arguloid family have been hitherto observed. 



I avail myself of this occasion to refute some objections which 

 have lately been put forward by Glaus* against the attempted 

 arrangement of the order Copepoda communicated by me in my 

 memoir above cited — "Contribution to our knowledge of the 

 Crustacea which live on the species of the genus Ascidia, h/'f 

 This arrangement (in three parallel series, Gnathostoma, Poeci- 

 lostoma^ and Siphonostoma) is based upon the structure of the 

 organs of the mouth, which, he says "in the first division are 

 adapted for chewing, in the other two for piercing and sucking. 

 The arrangement of the free and parasitic in parallel series 

 renders the formation of the subordinate groups more difficult, 

 the three forms of mouth presenting numerous cases of transi- 

 tion. It separates nearly allied forms, and, if strictly adhered 

 to, produces an unnatural and one-sided system. Further, the 

 character imputed to the Poecilostoraa — ' Os mandibulis et si- 

 phone carens, maxillarum paribus 3-1 (-0) instructum' — rests 

 on an error, since the mandibles are very well developed." 



To begin with the last remark, which seems to contain a charge 

 of especial weight, since it would appear that Claus represents 

 me as overlooking in the Poecilostoma the presence of the very 

 organs (the mandibles) on the presence or absence of which the 

 differences between the Gna;,hostoma and Poecilostoma depend. 

 That such, however, is not his meaning, is apparent from an 

 expression on p. 28, where we I'ead, " Here [in the Corycseidse] 

 the maxillse are reduced to very simple plates furnished with 

 several bristles, and have been regarded by Thorell as appendages 

 of the mandibles." In effect the differences between Clauses and 

 my notions of the oral organs of the Poecilostoma reduce themselves 



* Die frei lebenden Copepoden, p. 9. 



t Prof. Kroyer (Bidrag til Kundskab om Snyltekrebsene, p. 82) also, 

 but more summarily, attacks this attempt. As, however, he brings for- 

 ward no sufficient objection, either against the principle adopted or the 

 mode of its api)lication, but rather confines himself to bitter invectives 

 against those zoologists who, not troubling themselves with " mere de- 

 scriptive work," are yet bold enough to " put forward systems," I shall 

 treat his criticisms as they deserve. 



31* 



