328 SYNOPTIC COLLECTION. 



have disappeared and the appendages are for the most 

 part jointless and lobe-like. The antennae are tiny and 

 indistinctly jointed (Baird). The mouth parts are 

 adapted for piercing and sucking, instead of for biting 

 as in non-parasitic Copepods. 



Another parasitic form of this group is Penella (No. 

 806), which bores into the body of a fish and lives partly 

 imbedded in the flesh. Its long, tubular body is indis- 

 tinctly segmented. At the anterior end there are several 

 pairs of vestigial appendages, while at the other extremity 

 a large number of thread-like organs extend beyond the 

 end of the abdomen and give a plume-like aspect to this 

 part of the body. 



One of the most modified Copepoda is Lernea bran- 

 chialis Linn. (No. 807 ; PL 808, figs, i, 2, drawings of the 

 same), found on the gills of codfish. Parasitism has 

 brought about such complete changes in this species that 

 it is only the young stage (fig. i) which enables one to 

 place it among the Crustacea. In this stage it is seen to 

 have a cephalothoracic region with a pair of eyes and 

 three pairs of jointed appendages. 



The body of the adult (No. 807 ; PL 808, fig. 2) has 

 lost all trace of segmentation and is an S-shaped sac with 

 two long egg masses hanging from it. There are no eyes 

 and no jointed appendages, the antennae even having dis- 

 appeared. The mouth parts are horny, root-like organs 

 which are buried in the flesh of the fish, and the fluid 

 food is obtained by suction. 



Phyllopoda. The group of Phyllopoda is of special 

 interest since it contains two genera, the brine Artemia 

 and the fresh-water Branchipus, which have been trans- 

 formed the one into the other, by changing their envi- 

 ronment. 



Artemia salina M. Edw. lives in salt lakes. By gradu- 

 ally decreasing the density of the salt water during sev- 

 eral generations, it has been converted into the fresh- 

 water genus Branchipus. By increasing the density of 



