33-' ARTHROPODA 



parapodia, (.lilTcring in 1 icing ioinlcil to die bodv, in consisting ol a scries of 

 joints tlicmscKcs. and in ha\ing tlicir intrinsic ninsculatufc. Tltcrc is hut 

 a pair of appendages to a somite, and tliis belongs to the \entral surface, 

 licnec it follows i^Sa\"ign\''s law) that although a rcgiotr may show no 

 external sigirs of segmentation, if it hear more titan one pair of appeirdagcs, 

 we conclude that it is a complex of at least as many somites as tJiere are 

 pairs of appendages. Titus the uirscgmenled head of an insect consists 

 of four somites, the cephalothorax of a lobster of tliirteeir, for the one bears 

 four, tlae other tliirteen, pairs of apipendages. Ontogeny supports tlu's, for 

 in the eml.n-yo the somites are clearly visible. This statement is i^ot ex- 

 acdv correct, for in certaiti insects and in the lobster there is orie more 



Fie. 307. Fio. 308. 



Fig. 367. — Pahrmon scrrjtus (from I,U(i\vit;-Leunis\ .1, abdomoii; Ct, ccphalo- 

 thor:i\ 



Fig. 30S. — Caiiidsiis coU-oplratonim (from Tasclicnbcrg'). 



somite wliich is entirely lost in the adult. It is not ncccssarv that each 

 somite in (he adult should bear appendages, since these may disappear 

 in growth without leaving a trace. 



Wliile originally all were locomotor, the appendages subserve many 

 functions (hg. 360). Locomotor appendages (pcrciopoda. feet or legs) 

 arc long and consist of a numlier of joints which mav form llattened oars 

 or may be provided with claws for creeping (S). Besides locomotor ap- 

 pendages there are tactile appendages or antcumc (\), chewing appendages 

 (jaws, maiidiblvs, ma.xilhc, 2-j,). false feet ox plcopoda (o) of \-arying func- 

 tions, and forms— ,v;j.v/////>c</,s' (5-7)— transitional between jaws ami legs. 



Aside from being tactile, antenna- are characterized by ]iosition and in- 

 nervation. They are always iir front of the mouth and receixe their nerve 

 supply from the supraa'soi)hageal ganglion, while all other appendages 



