CALIGOIDEA. 



1319 



The abdomen has from one to three segments; the number is 

 usually two. In Argulus (fig. 2 a, b, Plate 94), only one segment is 

 distinct; this one is deeply two-lobed behind, and at the bottom of the 

 sinus separating the lobes there are two minute appendages, which are 

 rudiments of a pair of caudal stylets. In Caligus, the abdomen has a 

 large basal segment, following which there are one or two much 

 narrower segments. The basal segment in females with eggs is larger 

 than in males, and of different form ; and at its posterior angles it 

 bears the oviferous tubes. It hence follows that this basal segment is 

 the homologue of the second, or first and second abdominal segments, 

 in the Cyclopoidea ; for the second is normally the egg-bearing seg- 

 ment throughout that tribe. In males, the posterior angles are often 

 projecting, and are sometimes furnished with two or three very short 

 setae ; the same setae may occur in females. 



In Dinematura, Cecrops, and Lepidopus, the abdomen has but two 

 segments, and though very large, the second segment is quite small, 

 and is situated beneath the preceding, near its extremity. The caudal 

 stylets in Caligus and allied genera are much like those in the Cyclo- 

 poidea, and have the same number and arrangement of setae. In 

 Lepidopus, they appeared to be wanting, being represented by very 

 small lobes on the hinder margin of the last abdominal segment. 



Appendages of the body.— The figures on Plate 92, represent in 

 parallel columns the different forms of these organs among the prin- 

 cipal sections of the Caligoidea, together with the same in Sapphirina 

 and Corycaeus for comparison.* 



The anterior antennas in the Caligidae are short, and consist usually 

 of but two joints (l, in fig. 1 a, and 1 r, Plate 93). The first joint has 

 a number of short setae along the anterior margin, which are setulose, 

 and each receives a branch of the antennary nerve. These setae 

 shrink up on drying, and thus differ from the setae of the body. The 

 second joint has only a few naked setae ; there is a single seta at the 

 middle of the posterior side ; also a lower and an upper apical set, the 

 former of which are a little the longer and more acute. The frontal 

 segment of the cephalothorax in Caligus and the allied genera is pro- 

 bably the basal portion of these antennae, and if counted as such, the 

 organs would be three-jointed. In Laemargus, this frontal segment is 



* Of the figures of this plate, 1 a, b, etc., represent organs of Sapphirina; 1 a', b' f 

 etc., ibid, of Corycaeus; 2, of Argulus; 3, of Caligus (3 k' of Calistes); 4, of Pandarus; 

 5, of Lepidopus; 6, of Dichelestion; 7, of Chondracanthus. 



