No. 2194. NORTH AMEICWAN PARASITIC COPEPODS— WILSON. 107 



and buries its head in some vital organ, forming an enormous cyst, 

 which becomes very hard and remains a long time after the death of 

 the parasite ; it always shows torsion and sometimes flexion. 



External generic characters of C'opepodid 7nale. — Cephalothorax 

 made up of head and first thorax segment fused ; second, third, and 

 fourth segments free and diminishing gradually in width ; fifth and 

 genital segments fused; abdomen one- jointed, anal laminae short and 

 wide. 



First antennae indistinctly jointed and well armed with setae; 

 second pair two-jointed with a stout chela; mouth tube long and 

 barrel-shaped; mandibles without teeth; first maxillae on the out- 

 side of the tube at its base, bilobed ; second maxillae on the ventral 

 surface of the head, two-jointed and tipped with a claw ; maxillipeds 

 near the posterior margin of cephalothorax, also two- jointed and 

 tipped with a claw; swimming legs corresponding exactly with those 

 of the female ; no fifth legs. 



Internal generic characters of Copepodid male. — Esophagus short 

 and strongly inclined to the body axis; stomach much widened in 

 the cephalothorax, tapered posteriorly and passing insensibly into 

 the narrow intestine. Supraesophageal ganglion comparatively 

 small, connected dorsally with a wide tripartite eye and anteriorly 

 with a large frontal gland secreting an attachment filament. Infra 

 ganglion almost as large as the stomach and extending back into the 

 second thorax segment. Testes paired and opposite each other above 

 the stomach in the first and second thorax segments, ovate, with 

 wide sperm ducts leading back to large spermatophore receptacles 

 in the genital segment. 



Type of the genus. — Pennella sagitta (Linnaeus), first species. 



(Pennella, diminutive of Penna-, a feather). 



Remarks. — This genus has been probably the least understood of 

 any in the entire family and scarcely any two authors have described 

 their species similarly. This is partly due to the fact that speci- 

 mens are often mutilated in order to save the host, since the removal 

 of a Pennella in its entirety is almost certain to involve the destruc- 

 tion of its host as a museum specimen. It is also partly due to the 

 presence of a much larger and tougher cyst around those portions 

 of the body which are buried in the host ; this is very difficult to re- 

 move without injury to the parasite. Again the short and stubby 

 frontal processes, like those on a cauliflower, entirely cover the 

 mouth and surrounding regions, and several heads must be sacrificed 

 before gaining an adequate idea of the structure of the buccal re- 

 ' ion. In the present instance there has been an abundance of ma- 

 terial for clearing in clove oil, for dissection, and for sectioning, and 

 the facts here presented have been ascertained in all these ways as 

 well as by ordinary methods. 



