29 



by a layer of protoplasm, wliicli separates it from the 

 sarcoleinma or sbeatli. 



Xervous System a^d Sexse Organs. 



The nervous system consists of a paired chain of 

 g-anglia, each pair of gang-lia being- united to the next by 

 two distinct cords. The first, or supra-oesophageal 

 ganglion, which forms the brain (PI. II., hr.), lies imme- 

 diately below the eyes, and is connected with the ventral 

 nerve chain (PI. II., n.c.) by a perioesophageal nerve ring 

 (PI. II., pert. 11. )'.). In the brain, as in the other 

 ganglia, there are, as Packard (15) observed in Asellus, 

 three kinds of elements. — (1) Ganglion cells, with large, 

 deeply-stained nuclei, which are grouped round the 

 ganglion in pyramidal masses, the bases of which are 

 applied to the ganglion ; (2) nerve hbres which arise from 

 the ganglion cells and connect the ganglia; (■^>) myeloid 

 tissue or substance (the " punktsubstanz '" of Leydig), in 

 which the nerve fibres are embedded, and which forms the 

 mass of the ganglion. 



The brain (PI. II., hr.), which has been vcr}' fully 

 described and figured by Koehler (9), is a syncerebrum, 

 consisting of (1) two large superior lobes, to the external 

 extremities of which are attached the optic lobes con- 

 nected with the retina by parallel nerve fibres, (2) two 

 smaller median lobes, (■')) two large inferior lobes, named 

 by Koehler the " olfactory lobes," each with a lateral 

 olfactoiy bulb, which appears to be an aggregation of 

 spherical masses of myeloid tissue. Some fibres from 

 both median and iiiferior lobes ])ass to the superior lobes, 

 those from the inferior lobes intercrossing- to form a 

 chiasma. Into the inferior lobes run the nerves from the 

 first antenna-, and, a little further back, those from the 



