CALIGOIDEA. 1325 



some Caligidae it is simply two-branched and natatory in character. 

 In other Caligidae it is a broad plate, with two small one-jointed mar- 

 ginal appendages much like the third pair; and in others — the' true 

 Caligi — there is but a single branch, and the leg is rather slender, and 

 ends in a long spiniform finger with also one or two shorter spines 

 below, being wholly without plumose setae, and having no natatory 

 character. The finger is minutely pectinated along its inner margin. 



Eyes. — The eyes are either simple or compound, being simple in the 

 Caligidae and compound in the Argulidae. In Caligus, the two simple 

 eyes are placed on the same spot of pigment and have spherical lenses, 

 resembling the superior eyes of the Cyclopoidea. The shell above 

 the eyes is flat. Below it, over the eyes, there is a cornea, thin and 

 transparent, about twice the diameter of the lens. 



Besides the ordinary simple eyes in the Caligidae, there is some- 

 times a pair of simple eyes with large prolate lenses and oblate con- 

 spicilla or broad convex corneas, like those of the Corycaeidae, as in 

 our genus Specilligus. The presence of this kind of eyes is not at- 

 tended by any marked peculiarities in the structure of the species, 

 analogous to that separating the Corycaeidae from the other Cyclo- 

 poidea, and consequently the character is not to be received as a 

 family distinction, though a proper basis for a subfamily division. 



Muscular System in Caligus. — The muscles moving the several 

 members, may, in general, be distinctly seen and traced to their inser- 

 tions, through the pellucid covering of the body. All the muscles 

 appear transversely striated, and by means of this important cha- 

 racter, they are distinguished from the nerves. These striations are 

 most distinctly seen in the flat, simple muscles; those composed of 

 several bundles of fibres, which is the case with many of the large 

 muscles on the back, exhibit it, but less perfectly. These striations 

 vary much in their fineness. In general, they are from 71 ^ to BJ * VJi 

 of an inch apart. In some muscles, among which we may mention 

 those elevating the buccal mass, we found them as coarse as ^^ of 

 an inch. 



On account of the peculiar forms and motions of some of the organs 

 in this animal, it contains several muscles of unusual character. 



a. Muscles of the Segments of the Body. — The frontal segment is 



332 



