CALANOIDA. 



The chief characters of this great division have been well pointed out by 

 Dr. Giesbrecht, and consist in the firm conjunction of the last pedigerous segment 

 with the proceeding one, with which it is not infrequently even wholly coalesced, 

 whereas in most other Copepoda this segment forms a very movable articulation 

 with the former, and is firmly connected with the 1st segment of the urosome, 

 thus giving it the appearance of belonging more properly to that section of the 

 body. In all the forms the anterior division of the body, comprising the cepha- 

 losome and metasome, is much broader than the posterior (urosome), which is 

 abruptly narrowed and very movably connected with the former. The female 

 genital openings occur generally close together on the ventral face of the 1st 

 caudal segment, whereas in the male only a single such opening is found lying 

 asymmetrically, generally on the left side. 



As to the several appendages, the anterior antenna? are as a rule much 

 elongated, sometimes of the very same appearance in the two sexes, but more 

 generally transformed in the male, either by a reduction of the number of articula- 

 tions combined with a much more abundant supply of the peculiar sensory appen- 

 dages named by Dr. Giesbrecht "aesthetascs", or by a geniculated structure of 

 one, generally the right, antenna. The posterior antenna are always biramous, 

 with the inner ramus (endopodite) biarticulate, the outer (exopodite) multiarticulate, 

 though the latter, in some cases, is much reduced in size. The mandibles generally 

 have the masticatory part exceedingly dentate, and are provided with a well- 

 developed biramous palp, which, like the posterior antennae, is subservient to 

 locomotion. The maxillae generally exhibit a rather complicated structure, though 

 the same chief parts as in the 2 preceding pairs of appendages may easily be 

 demonstrated, with the addition of 3 setiferous lobes, the generally large vibratory 

 plate outside the basal part, and the 2 much smaller appendicular lobes occur- 

 ring close together inside between the basal part and the palp. The 2 pairs of 



