490 



COPEPODA. 



large number of secondary characters. So far as is known a more or less 

 modified Nauplius larva is usually preserved. 



The development of Achtheres percarum, one of the Lernaeopoda parasitic 

 in the mouth, etc. of the common Perch, may be selected to illustrate the 

 mode of development of these forms. The larva leaves the egg as a much 

 simplified Nauplius (fig. 230 A). It has an oval body with only the two 

 anterior pairs of Nauplius appendages ; both of them in the rudimentary 

 condition of unjointed rods. The usual median eye is present, and there is 

 also found a peculiar sternal papilla, on which opens a spiral canal filled 

 with a glutinous material, which is probably derived from a gland which 

 disappears on the completion of the duct. The probable function of this 



FIG. 230. SUCCESSIVE STAGES IN THE DEVELOPMENT OF ACHTHERES I'ERCARUM. 

 (Copied from Bronn ; after Claus.) 



A. Modified Nauplius stage. B. Cyclops stage. C. Late stage of male 

 embryo. D. Sexually mature female. E. Sexually mature male. 



at 1 , first pair of antennae ; at 3 , second pair of antennas ; nid. mandible ; nix. 

 maxilla;; />/'. outer pair of maxillipeds ; pnP. inner pair of maxillipeds; /'. first pair 

 of legs ; /*. second pair of legs ; z. frontal organ ; i. intestine ; o. larval eye ; b. 

 glandular body ; /. organ of touch ; ov. ovary ; f. rod projecting from coalesced maxil- 

 lipeds ; g. cement gland ; rs. receplaculum seminis ; n. nervous system ; te. testis ; v . 

 vas deferens. 



organ is to assist at a later period in the attachment of the parasite to its 

 host. Underneath the Nauplius skin a number of appendages are visible, 

 which become functional after the first ecdysis. This takes place within a 

 few hours after the hatching of the Nauplius, and the larva then passes from 



