464 



COMPARATIVE ANATOMY 



CHAP. 



The number of Malpighian vessels is occasionally smaller in the larva than in the 

 adult. Thus the larva of the Honey bee (Fig. 321) has only 4 vessels. In the 

 Blattidce and Gryllidce the number increases during the gradual development. In 

 the Lepidoptera the larva usually possesses the same number as the adult. Among 

 the Termites only do the young forms possess more numerous Malpighian vessels 

 than the adults. 



V. The Nervous System. 



This appears in the form which is characteristic of the Arthropoda 



and consists of the brain (supra - 

 oesophageal ganglion), the cesophageal 

 commissures, and the ventral* chord. 

 The brain, which lies in the head 

 above the oesophagus, often attains to a 

 high degree of development (especially 

 in the highly developed Hymenoptera), 

 and is distinguished by the formation 

 of lobes (ganglion opticum, olfactory 

 lobes, etc.) From it arise the nerves 

 for the sensory organs which lie in 

 the head, for the eyes, the antennae, and 

 the olfactory organs on the antennae. 

 We can always distinguish in the 

 ventral chord a cephalic and a trunk 

 portion. The former consists of the 

 infra -oesophageal ganglion, composed 

 of the fused ganglia of the oral limbs, 

 which in the embryo are often separate. 

 The trunk portion of the ventral chord 

 must originally have consisted of as 

 many double ganglia united by longi- 

 tudinal commissures, as there are trunk 

 segments, but the ganglia of some of 

 the last trunk segments are always 

 fused to form a terminal ganglion, 

 generally somewhat larger in size than 

 the rest. The ventral chord is found 

 in this unconcentrated form in the 

 Myriapoda, Apterygota, and many Ptery- 

 gota, and especially in the larvae of the 

 Hexapoda. We find, however, within 

 various orders of the Hexapoda more 



a, Antenna* ; fc/, maxillipedes (poison feet); or l ess pronounced Concentration of 



the ventral chord in a way similar to 

 that described in connection with the 

 Crustacea. This concentration takes place by the fusing of pairs of 

 ganglia it may appear in the abdomen as well as in the thorax and 



FIG. 323. Lithobius forficulatus seen 

 from the ventral side (after R. Leuckart). 



sd, salivary glands ; bm, ventral chord ; cp, 

 coxal pores. 



