NO. 1-104. PARASITIC coPEPODs—( A Lra Ti>:i:—w risox. 539 



the iulult stai^'C is n('\'<'r t'oiiiid on the outside^ surface of" tlu' body or 

 on the tins, but tlioso arc the v<m'v phu-es most easily accessible to the 

 young uietanauplius and ^vher(^ consecpiently it nuist be sought. 



And then the larvae are so small as alnu)st to re((uire a hand lens for 

 i-ecognition, and their color is so similar to that of the tislTs Ixxly as to 

 afford them ample proti^ction. 



About the only way to detect them in most cases is to take the fish 

 tlirectly from the wat(M', and while it still retains a film of water over 

 the entire outside of the l)ody hold it up to the lioht in such a way as 

 to o-et the rays reflected from the surface. The larva, l)einn- attached 

 loosely, stands oH' frou) the surface and l)reaks the reilection. If the 



Fig. .38. — N.iUPLius of Caligus kon'ito nearly ready to moult into .v METANAi'i'Lius. The 



PIGMENT, WHICH AT FIR8T WAS IN A CONTINUOUS RING, IS NOW BROKEN ITP. VENTRAL VIEW, 

 SHOWING LABRUM. 



fish has been dropped to the ground or into the bottom of a, boat there 

 is very little use to search it for development material. 



In view of these difficulties it is not surprising that so few larval 

 stages have been secured hitherto, or that investigators o\'erlooked all 

 but the largest and most advanced embryos. 



As has been stated the nauplius attirst is entirely unsegmented, with 

 the three pairs of appendages grouped around the mouth near the 

 anterior end of the body. The first moult occurs during the first 

 thirt3'-six hours, usually in the night; the nauplius emerges with its 

 body considerably elongated and with the evident beginnings of seg- 

 mentation posteriorly. The division between liead and thorax is 

 plainl}^ indicated in the clear edge which borders the carapace (tig. 37). 



