352 



ARTHROPODA 



parapodia, differing in being jointed to the body, in consisting of a series of 

 joints themselves, and in having their intrinsic musculature. There is but 

 a pair of appendages to a somite, and this belongs to the ventral surface. 

 Hence it follows (Savigny's law) that although a region may show no 

 external signs of segmentation, if it bear more than one pair of appendages, 

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

 pairs of appendages. Thus the unsegmented head of an insect consists 

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

 four, the other thirteen, pairs of appendages. Ontogeny supports this, for 

 in the embryo the somites are clearly visible. This statement is not ex- 

 actly correct, for in certain insects and in the lobster there is one more 



FIG. 367. Pal(pmon serratus (from Lud \vig-Leunis). A, abdomen; Ct, cephalo- 

 thorax. 



FIG. 368. Gamasus coleoptratorum (from Taschenberg). 



somite which is entirely lost in the adult. It is not necessary that each 

 somite in the adult should bear appendages, since these may disappear 

 in growth without leaving a trace. 



While originally all were locomotor, the appendages subserve many 

 functions (fig. 369). Locomotor appendages (pereiopoda, feet or legs) 

 are long and consist of a number of joints which may form flattened oars 

 or may be provided with claws for creeping (8). Besides locomotor ap- 

 pendages there are tactile appendages or antenna (i), chewing appendages 

 (jaws, mandibles, maxilla, 2-4), false feet or pleopoda (9) of varying func- 

 tions, and forms maxillipeds (5-7) transitional between jaws and legs. 



Aside from being tactile, antennae are characterized by position and in- 

 nervation. They are always in front of the mouth and receive their nerve 

 supply from the supracesophageal ganglion, while all other appendages 



