186 



Arthropoda. 



{Pig. 148). They are thrown off with the rest of the cuticle at 

 each moult and renewed. The muscular tissue of the Arthropods 

 consists of striated^ multinucleate muscle fibres. 



Fig. 147. 



Fig. 148. 



Fig. 147. The last four joints of an arthropod limb with their muscles : diagrammatic. 

 I articulation, B and 6 flexors, 8 and s extensors, u. places where two joints touch one 

 another, and the articular membrane is very narrow ; 1 terminal, 2 penultimate joint, etc. 

 — Orig. 



Fig. 148. Longitudinal section through a j o i n t of an Arthropod : diagrammatic. 

 c cuticle, ep epidermis, I articular membrane, M muscle, o opening of the tendon to which 

 the muscle is attached. — Orig. 



The nervous system agrees closely with that of the Annelids. 

 Just as in these animals there is a pair of ventral ganglia in each 

 segment, connected with those of the adjacent segments by a double 

 nerve cord. Prom the most anterior of these ganglia spring two nerve 

 cords, which run round the oesophagus to unite with a paired 

 ganglion mass, the cerebral ganglion, lying in the head. This 

 often attains to a very considerable size, which is correlated, amongst 

 other things, with the development of certain sense organs, situate on 

 the head, the compound eyes. The ventral ganglia often exhibit 

 remarkable differences from those of the Annelids, differences which 

 are due to the above-mentioned dissimilarity in the formation of the 

 segments and their grouping into different regions. In well-developed 

 segments for example the ganglia are large, whilst a fusion of many 

 segments is accompanied by a fusion of their ganglia. In some cases. 



