538 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxvin. 



which usually point obliquely backward, and are of peculiar .shape. 

 Cylindrical at the base for about one-fifth of their entire length they 

 then flatten antero-posteriorly and broaden slightly into the shape of 

 a spatula or paper cutter. 



They are not segmented and not readily movable; they seem to be 

 used as a kind of balancing organ when the nauplii assume an upright 

 position in the water on coming to rest. . 



The uniformity in the shape of these balancers as well as that of the 

 bod} 7 of the nauplii and the three pairs of appendages is good evi- 

 dence of the close relationship of the genera here considered. 



If a female be captured with eggs nearty or quite matured it is an 

 easy matter to secure nauplii by keeping her over night in cool water. 

 But to rear the nauplii suceessf ully is a very different matter for many 

 reasons. 



In the first place they are extremely sensitive to even a slight rise in 

 temperature and of course can not be kept in an aquarium of running- 

 water, and as they advance toward the chalimus stage they require 

 f reshl} 7 aerated water far more than in the nauplius stage, which it is 

 exceedingly difficult to supply properly. A great many different 

 methods have been tried, but the best success thus far has been 

 obtained by keeping the larva? in floating aquaria or bags of cheese 

 cloth, immersed in the ocean. The mouth of the bag is open and it is 

 floated at a sufficient height above the surface of the water to prevent 

 the washing out of the larvae. 



As the latter natural^ swim at the surface, this insures just the 

 right temperature. And if they eat anything prior to the metanauplius 

 stage, which is very doubtful, apparently enough food gets in through 

 the meshes of the cheese cloth to keep them alive. In this way the 

 nauplii of two species of Caligus, O. rapax and C. bonito, and one 

 species of Lepeophtheirus, L. edwardsi, have been carried through 

 several moults. 



But of course when they reach the stage at which they would ordi- 

 narily fasten upon some host, all artificial methods fail, and we must 

 depend for further material upon a careful examination of the fish's 

 body. To achieve any success demands a knowledge of two things, 

 the particular host or hosts preferred by any given parasite and the 

 time of breeding. By securing a plentiful supply of the host just 

 after the parasite's eggs have hatched one ma} 7 be reasonably sure of 

 finding some larva? attached to them. 



But obviously the securing of these early stages will require a very 

 minute examination of every part of the fish's body, since the larva 

 apparentl} 7 fastens itself to the first place it happens upon, and may 

 show no indications whatever of a preference for particular localities, 

 which later in life becomes very marked. Especially is this true of 

 such species as frequent the mouth and gill cavity. Caligus honito in 



