no. 1 104. pa RASITIC COPEPODS— CALIGIDJE— WILSON. 591 



Color a pule transparent yellow without any pigment, except at the 

 tips of the lateral lobes and the adjacent thoracic area, which are 

 thickly spotted with light, rusty brown. 



The copepod thus appears as if it had two large brown eyes, one on 

 either side of the body at the posterior end of the carapace, and it may 

 be readily recognized by these, since no other species is marked simi- 

 larly. 



(bonito, the name of its host.) 



Male. — Considerably different from the female. The carapace is 

 more nearly orbicular, while the thoracic area is much narrower 

 (^. 152). 



This gives the posterior end of the carapace a rounded appearance 

 quite different from the truncate look of the female. 



The free thoracic segment is much wider posteriorly than anteriorly, 

 and projects so far beyond the sides of the genital segment that the 

 fourth legs are attached to its posterior rather than its lateral margin. 

 Tin 1 genital segment is but little wider than the abdomen and quite 

 fusiform, the anterior end being usually well wrinkled. The abdomen 

 is the same length as the genital segment and is jointed once near the 

 center. 



These alterations in shape produce equally marked changes in the 

 proportions of the various parts. Whereas in the female the propor- 

 tion in length between the cephalothorax and the remainder of the 

 body (exclusive of the egg strings) is as 7 to 10; in the male the same 

 proportion is as 7.5 to 6.5. This change is far more than usual. The 

 first antennae are relatively larger and longer than in the female, this 

 being particularly true of their basal joints with the lunules. 



The second antennae are not as stout as those of the female, but the 

 first maxillae are nearly three times as large. This makes the two 

 appendages in the male nearly the same size, the maxillae being a trifle 

 longer but not as stout. 



In tin 1 second maxillipeds the basal joint is reinforced at its distal end 

 by a thick, bony plat* 1 on the inner side. The powerful terminal claw, 

 folding down against this plate, makes a very effective clasping organ. 



Total length, 5.5 mm. Length of carapace, 3 mm.; width of same, 

 2.8 mm. : length of genital segment, 1 mm. ; length of abdomen, 1.2 mm. 



Wauplius. The newly hatched nauplii are large and active. They 

 are rather elongate in form, the length being nearly three times the 

 width, and the body is bluntly rounded both anteriorly and posteriorly 

 dig-. :'>T. 38 in text). The three pairs of appendages have the typical 

 nauplius form. The labrum is oval in outline, with a broad, shallow 

 sinus on cither side and in front, but with a wide, blunt projection 

 posteriorly. The body is pigmented with rusty brown in narrow 

 patches all along either side and posteriori} 7 , the patches being irregu- 

 larly disposed. Sometimes these pigment patches are fused into an 



