394 



INVERT EBRA TE MORI >I10L OGT. 



appendage separates into two portions inserted separately 



into the body-wall. The an- 

 terior one is a comparatively 

 small plate provided with 

 numerous masticatory setae on 

 its inner edge, while the 

 posterior is an elongated 

 limblike structure. It is this 

 combination of a maxillary 

 and limblike portion that has 

 gained for this appendage the 

 term maxilliped, though it 

 must be recognized that it is 

 a true cephalic appendage and 

 not comparable to the inaxil- 

 lipeds of the higher forms. 

 The five thoracic appendages 

 (t l 5 ) are typically biramous 

 and serve for swimming. 



This description refers to 

 the free-swimming forms ; in 

 parasitic species much modi- 

 fication of the appendages 

 ensues. The antennules lose 

 their long oarlike character 

 and may even be degenerated 

 to strong hooks which serve 

 to fasten the animal to its 

 host, a degeneration which 

 the antennae may also under- 

 go. The mouth-parts become 



FIG. ITI.Calanus hyperboreus (after adapted to a piercing func- 



GlESBRECHT). 



an = anus. 

 at [ = auteunule. 

 at* = antenna. 

 mn = mandible. 



mx l , mx 1 first and second maxillae. 

 P-p = thoracic appendages. 



thus produced. The first 



tiou, and the mandibles are 

 represented b}^ sharp stylet- 

 like structures, sometimes en- 

 closed in a tube formed by the 

 union of the upper and lower 

 lips, a sucking-organ being 

 maxillae undergo considerable 



