CRUSTACEA. 



405 



typical Nauplius 1 . There are slight variations in the shape of the Nau- 

 plius in different genera, but its general form and character are very 

 constant. It has (fig. 229 A) an oval unsegmented body with three 

 pairs of appendages springing from the ventral surface. The anterior 

 of these (at\] is uniramous, and usually formed of three joints which 

 bear bristles on their under surface. The two posterior pairs of 

 appendages are both biramous. The second pair of antennae (at 2) 

 is the largest. Its basal portion (protopodite) bears on its inner 

 side a powerful hook-like bristle. The outer ramus is the longest 

 and many-jointed ; the inner ramus has only two joints. The 

 mandibles (md), though smaller than the second pair of antenna?, 

 have a nearly identical structure. No blade-like projection is as yet 

 developed on their protopodite. Between the points of insertion of 

 the first pair of antennae is the median eye (oc), which originates by 

 the coalescence of two distinct parts. The mouth is ventral, and placed 

 in the middle line between the second pair of antennas and the man- 

 dibles : it is provided with an unpaired upper lip. There are two 

 bristles at the hind end of the embryo between which the anus is 

 placed, and in some cases there is at this part a slight indication of 

 the future caudal fork. 



The larva undergoes a number of successive ecdyses, at each of 

 which the body becomes more elongated, and certain other changes 



\\, A 



aei 



D 



FIG. 229. SUCCESSIVE STAGES IN THE DEVELOPMENT OF CYCLOPS TENUICOBNIS. 



(Copied from Bronn ; after Claus.) 



A, B. and C. Nauplius stages. D. Youngest Copepod stage. In this figure maxillse 

 and the two rami of the maxilliped are seen immediately behind the mandible ind. 

 oc. eye; a* 1 , first pair of antennae; at 2 , second pair of antennae ; md. mandible; 

 p 1 . first pair of feet ; p*. second pair of feet ; p 3 . third pair of feet ; u. excretory con- 

 cretions in the intestine. 



1 The term Nauplius was applied to the larva of Cyclops and allied organisms by 

 0. F. Miiller under the impression that they were adult forms. 



