484 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxvin. 



iiiid animal alike, namely, the original search for a suital^le host. But 

 this opei-atc^s in develo])niental rather than in adult stages, and it is a 

 siuiiiHcant fact in this connection that nearly ever}^ female of these 

 genera which has hcHMi captur(Ml in the tow has been immature. 



The mcM-hanical hindrance atfordiMl by the egg-string.s, together with 

 the strong incenti\es just enumerated for remaining upon the body of 

 the host, may ))e fairly considered as constituting the first step toward 

 degeneration. L(^t us now look at the mode of locomotion in these 

 genera in order to discover the second step. 



LOCX)M()Tr()N. 



There are two modes of locomotion as in the Argulidw, a free- 

 swimming :iiul a scuttling motion. The presence or absence of th(^ 

 latter has a greater significance than has hitherto l)een accorded to it. 

 By watching specimens of Arynlns and ('((J/<jiix in an a(|uarium it can 

 be seen that the latter are really the better swimmers. This is due 

 to the increased surface of the Hrst threc^ pairs of legs, particularly to 

 th(^ large lamina or apron which connects the third pair across the ven- 

 tral surface of the ))ody. These legs furnish a swimming organ which 

 ])ropels the copc^pod through the water with strong and swift move- 

 ments. Often the luotion is so erratic and persistent that the animals 

 seem to have fairly gone mad, dashing franticall_v about, turning sum- 

 mersaults, I'ushing for a distance along the sides of the aquarium, or 

 scuttling back downward across the under side of the surface tilm of 

 the water. E(iuipped with such a swimming apparatus it would nat- 

 urally be supposed that they would put it to frequent use, but we have 

 already" seen that they lack the incentive. Asa matter of fact, mature 

 females of but one or two species have ever been taken with the males 

 at the surface. 



Furthermore, as will appear in the descriptions wdiich follow, these 

 few specimens were all of the genus Cif//'(/us^ the species rapax being 

 most commonly secured. The otlun- genera here treated do not show 

 as nuich inclination to free swinnning as Caligux and there are but one 

 or two very doubtful records of their capture in the tow. Indeed, 

 A. Scott goes so far as to conclude from a series of car(>ful investiga- 

 tions that ''"LipeopIifJidriix throughout the remainder of its life and 

 under normal conditions n^nains on the same tish that it attached 

 itself to at tin; beginning of the chalimus stage. '' And the same might 

 proliabl}' be said with regard to Avvrcfi'H and Tnhii/s. 



When W(» consider the amount of surface towing conducted everv 

 year under the auspices of the United States Bureau of Fisheries, the 

 scarcity of these parasitic forms can only mean that at least the mature 

 females are not accustomed to swim freidy at tlie surface, but only do 

 so under extreme provocation. 



