464 



COMPARATIVE ANATOMY 



CHAP. 



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

 adult. Thus the larva of the Soimj bee (Fig. 321) has only i vessels. In the 

 Blattidcc 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 Artliropoda 



and consists of the brain (supra- 

 cesophageal ganglion), the oesophageal 

 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 Hijmenoiitera), 

 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 antennse, 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 larvse of the 

 Hexapoda. We find, however, within 

 various orders of the Hexapoda more 

 or less pronounced concentration of 

 the ventral chord in a M^ay 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). 

 a, Antennee ; kf, maxillipedes (poison feet) ; 

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

 eoxal pores. 



