10 BULM;TIN 158, UNITED STATES NATIONAL MUSEUM 



Each of the thoracic segments may bear a pair of legs, those on 

 the fifth and sixth segments being more or less modified and rudi- 

 mentary. In the free-swimming copepods the sixth pair is nearly 

 always lacking, and often also the fifth pair in the females, but both 

 pairs are often present in parasitic and semiparasitic forms, and in 

 the males of the free swimmers. 



At the posterior end of the abdomen there is a pair of appendages, 

 which are usually well armed with setae. In the free-swimming 

 copepods it has been customary to call them the furca, and each of 

 them a furcal ramus. But the name furca was applied more than 

 100 years ago to an organ on the ventral surface of Caligus and 

 allied genera of the Caligoida. This is not an appendage in the 

 same sense as the other organs already enumerated, but is unpaired 

 on the midline and aids in prehension. Accordingly in this report 

 the designation used by Sars will be adopted and this pair of 

 abdominal appendages called caudal rami. 



Classification adopted. — The classification here adopted was first 

 suggested 20 years ago by G. O. Sars. It is much the simplest 

 one ever offered and is the only one that furnishes a place for every 

 valid genus. Why not extend it to include the argulids as well as 

 the other copepods, and eliminate the usual division into Eucopepoda 

 and Branchiura? The latter suborder contains only the argulids, 

 and hence nothing is really gained by introducing a second name 

 for them. Moreover this second name, Branchiura, is a rank mis- 

 nomer because it perpetuates the mistaken idea that in the argulids 

 respiration is confined to the tail, while in the Eucopepoda it takes 

 place elsewhere in the body. In reality the exact reverse of this 

 comes nearer to the truth; the argulids have comparatively little 

 tail respiration, the true respiratory areas being situated in the 

 cephalothorax. On the contrary in the Eucopepoda the most im- 

 portant respiration takes place in the rectum, and there are no 

 respiratory areas in other parts of the body. This division of the 

 copepods therefore was false in its original conception, and has been 

 steadily growing more inaccurate, as our knowledge of the Crustacea 

 has progressed; is it not about time to discard it? If this be done 

 the order Copepoda may be divided directly into the following 

 eight suborders: Arguloida, Calanoida, Harpacticoida, Cyclopoida, 

 Notodelphyoida, Monstrilloida, Caligoida, and Lernaeopodoida. 



Copepod families. — With reference to the gathering of the genera 

 into families we find everywhere the greatest diversity of opinion. 

 Giesbrecht and Schmeil in Das Tierreich discussed all the genera 

 of the Calanoida that had been described up to that time (1898). 

 They divided the 65 genera that they considered valid into five fam- 



