The Development of Theridium. 321 



seen on longitudinal section in Figs. 89-9 la and on surface views in 

 Figs. 82, 83, 85 ; it has maintained its former position while the cheli- 

 cera have pushed forward to its leve]. The cerebral ridges of the earlier 

 stages have sunk beneath the surface to constitute the cerebral ganglia 

 (C'e. G., Figs. 83, 85, 87a, b, 89-91a) ; they lie further dorso-posterior 

 than the other parts of the brain, and each of them is curved, as best 

 shown in Figs. 85 and 91a. Between them and the rostral surface 

 lie the optic ganglia (Op/. G'., Figs. 83, 85, 89, 90) that have been 

 formed by the union of the antero-lateral and postero-lateral vesicles 

 (A. L. v., P. L. v., Fig. 87b). It is somewhat difficult to be sure of 

 the precise relations of these cephalic ganglia on account of the fold- 

 ing and invagination they have undergone, and on the surface views 

 rejiresented in Figs. 83 and 85 they are below the surface, and conse- 

 quently somewhat obscured. But Fig. 89 indicates their relations on 

 a longitudinal section, and Figs. 87a (in the j^lane of the stomo- 

 daeum) and 87b (anterior to this plane) on two oblique transverse 

 sections of one embryo ; the latter two figures show that the cheliceral 

 ganglia (Chel. G.) are nearest the midline and embrace the stomo- 

 daeum anteriorly and laterally, that the cerebral ganglia (Ce. G.) 

 adjoin these dorso-laterally, and that the optic ganglia (A. L. V., 

 P. L. F.) touch them ventro-laterally. All these ganglia, as those of 

 the thorax, are developing neuropile (shown in the drawings by 

 stippling). 



At this stage appear the antero-median eyes, as ectoblastic infold- 

 ings above the rostrum (il/. E., Figs. 89, 91a). 



In the thoracal region the legs exhibit about five joints apiece 

 (Figs. 81-86), and the maxillary j)rocess of the pedipalps is well 

 developed {Ped. M., Fig. 83). The dorsal surface view. Fig. 85, 

 shows how the bases of these extremities have moved much further 

 dorsad, and how by an ectoblastic dorsad growth the extraembryonic 

 region has become reduced to the narrow band of the heart (//). 



The abdominal region is shown on surface views in Figs. 81-80. 

 Boundary lines between its component segments are seen as divisions 

 in its lateral areas (Figs. 81, 84, 80) demarcating the anterior five 

 segments. Of the four pairs of abdominal appendages (Figs. 81, 82, 

 84, 80) the third and fourth pairs {Ah. 41), Ah. 5h) are much the 



