6 BRITISH COPEPODA. 



sidered as such, and their characters so taken note of 

 by all systematists. The process of development, 

 however, has been traced by Glaus, so as to leave no 

 doubt as to the true nature of the organs. 



APPENDAGES OF THE HEAD. The eyes in their simplest 

 form in Cyclops, for instance appear as a red or 

 black spot in the middle of the frontal region, directly 

 over the brain, with which they are connected by a large 

 nerve, the spot when closely examined being found 

 to consist of two lateral eyes, closely approximated 

 and embedded in a mass of pigment ; the visual part 

 of the apparatus is composed of two refracting bodies, 

 or crystalline cones, and when more highly developed 

 may possess numerous lenses, so as to form something 

 like a facetted cornea. In some cases the eyes are 

 widely separated, and have between them, in the 

 median line, a simple, globular, pedunculated eye 

 (PontelUnce) ; in other cases, as in some Corycceidce, 

 the median eye is very small, while the lateral eyes 

 are large, destitute of pigment, and consist of simple 

 highly refracting lenses. In some parasitic species 

 only are the eyes entirely wanting. In Pleuromma 

 there is a supplementary eye, consisting of lenses 

 with black pigment matter, on one of the thoracic 

 segments. 



The anterior antennce are usually large and conspicu- 

 ous organs, rising from hollows in the front of the 

 head on each side of the rostrum. They act in many 

 species (Calanidce, Cyclopidce) as very powerful swim- 

 ming organs, it being by their agency chiefly that these 

 animals propel themselves through the water; the 



