490 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxvih. 



On the contrary, they can withstand a very great decrease in tem- 

 perature. Scott states that the aquaria containing* Lepeophtheirus 

 />< ct oralis were frozen several times without injury to the parasites. 

 Although this experiment has not been tried upon other species, 

 there is no reason to doubt that they could withstand as severe cold. 

 Repeated trials have shown that the best way to keep these creatures 

 alive for any length of time, particularly during hot weather, is to 

 pack the aquarium or bottle in ice. Those species which are other- 

 wise prone to crawl up out of the water are much less likely to do so, 

 but seem content to remain beneath the surface. Possibly this dis- 

 agreeable habit may be connected ordinarily with a rise in temperature 

 of the water in the aquarium. 



SUMMARY. 



1. The females of the genera here discussed carry their eggs about 

 with them. This necessarily restricts their freedom of motion, but 

 not to a greater extent than in free-swimming forms. 



2. Added to the restriction, however, is a lack of incentive to free 

 swimming, since the parasite obtains its food upon its host and finds 

 there the best position for the aeration of its eggs. 



These two conditions combined constitute the first step toward 

 degeneration. 



3. These genera are really better swimmers than the Argulidae, 

 owing to the increased surface of their swimming legs, particularly 

 the third pair. But they do not ,exercise this ability nearly as often 

 as the Argulidas, for the reasons just stated. 



■i. In addition to their free swimming, the Caligus species also 

 exhibit the same scuttling motion as the Argulidas, and it is accom- 

 plished in a similar manner by means of the sucking disks on the 

 frontal plates. 



5. In other genera the sucking disks are absent, the scuttling 

 motion is impossible, and we find still less of an inclination for free 

 swimming. Careful observations indicate that these genera remain 

 throughout life upon the same fish to which they attached themselves 

 in the chalimus stage. 



6. As another consequence of the loss of the scuttling motion they 

 remain for long periods in the same position upon their host, moving- 

 only upon strong provocation. This fixity of position constitutes a 

 second step toward degeneration. 



7. For prehension we find the sucking disks in Caligus, and stout 

 claws upon the second antennae and the second maxillipeds in all 

 genera. The edge of the carapace also, supplemented by the broad 

 lamina connecting the third swimming legs, is flattened against the 

 supporting surface and functions as a large sucking disk. 



8. To prevent slipping backward under friction there are weak 

 spines upon the bases of the first swimming legs, and a stout sternal 



