274 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 39. 



Fig. 5.— First antenna of Ergasilus manicatus, showing 



THE rORM found IN THE ErGASILIN-E. 



more on the ventral than on the dorsal surface. Although this 

 family of Ergasilidse is so closely related to the free swimming cope- 

 pods, and although in the genus Ergasilus the male never becomes 

 parasitic, but remains a free swimmer throughout life, yet there is not 

 in these first antennse any trace of the locomotor function in the 

 female, or of the prehensile function in the male, which are so charac- 

 teristic of free forms. On the contrary, they are entirely sensory in 

 function, as is clearly shown in their armature and innervation. They 



are curved abruptly near 

 the base in two direc- 

 tions, upward and out- 

 ward, so that nearly the 

 entire appendage is vis- 

 ible in dorsal view. 



They are made up of 

 joints which are indis- 

 tinctly separated near the base of the antenna, and in most species 

 there is more or less fusion here as a result (fig. 5) . 



We find the number of joints in these antennse variously given, 

 three for some species of Bomolochus (denticulatus) , four for other 

 species of Bomolochus (bellones and parvulus), five for the genus 

 TJiersitina, six for nearly every species of the genus Ergasilus, and 

 seven for a few species of Bomolochus (onosi, solese, etc.). But this 

 disparity is probably due to the indistinct separation of the basal 

 joints which is most manifest in 

 the fully developed adult. And we 

 may give the number as the same 

 in all the genera and species except 

 Thersitina, namely six, a basal por- 

 tion made up of three indistinctly 

 separated joints and three termi- 

 nal joints well defined and clearly 

 separated (fig. 6). 



In Thersitina there are but five 

 joints, all distinctly separated, and 

 this constitutes a good generic character (see p. 349). Each joint is 

 armed with setse, the longest of which are often as long as the entire 

 appendage. In the genera Bomolochus and Artacolax the basal 

 joints are enlarged, well fused and furnished with a heavy fringe of 

 stout plumose setae along their anterior margui. Interspersed with 

 these setse are tactile hairs without plumes, which are often as long 

 as the entire antenna. In some species {Bomolochus triceros, Arta- 

 colax scomberesocis, etc.) a process is given off from the ventral 

 surface of the basal joint which terminates in two or three large 



Fig. 6.— First antenna of Bomolochus emi- 

 nens, showing the form found in the Bo- 

 molochin^ and tieniacanthin^ 



