ON THE DEVELOPMENT OF AKANEIXA. 7i) 



of the legs. Unfortunately I could not find any trace of such an 

 organ, though I carefully searched after it. 



The development of the pigment begins from the cephalic region 

 backwards, after the ditferentiation of the vitreous Ijody (fig. 51). In 

 the case of the ' Nebenaiigen ' the pigment is first priKluced in those 

 cells which form a kind of a cup around the retinal portion (figs. 

 51-53), and it seems to me most probable that these cells wander in 

 to the retinal portion, first jtmong the nerve fibres beneath the 

 ta[)etimi (fig. 53), then among those above thetapetum (fig. 54). In 

 the case of the posterior median eyes, however, the pigment is pro- 

 duced from the beginning in retinal cells, below the vitrecnis body. 



As we have already seen, all the eyes of the spider are formed in 

 the ventral plate and near its anterior margin. 



The concentration of the nervous system towards the céphalo- 

 thorax goes on further in this stage than in the previous stage. In 

 the thoracic region the two lateral oanplionic chains are united into 

 one and form the subœsophagcal ganglion. The inner portion of the 

 ganglion becomes finely fibrous. The abdominal ganglia gradually 

 atrophy and attach themselves to the posterior end of the subœso- 

 phageal ganglion. At this stage the whole nervous system is com- 

 pletely cut off from the ectoderm. 



The stonioda'uni has devchjpcd very mucli. After chjiigating 

 itself obliquely upwards, it takes the horizontal backward direction and 

 reaches to about the segment of the fourth ambulatory a[)pendage. It 

 is lined with a cuticular covering which is continuous with the cuticula 

 <jf the general body surface. In the pliarynx, the cuticular lining is 

 tliick and transversely ridged. The ridges rim parallel with each other 

 and appear in the sagittal section like teeth, the pointed edge turning 

 dorsalwards. The wall of the stomodieum is very thick. The stomo- 

 dieum gives rise to the pharynx, the œsophagiis, and the st<jmach. 



