440 Avery E. Ijiiiiibert. 



by means of a sheet of ectoderm which forms the inner layer of the 

 cephalic fold. (Text-figure 3, ret.) The posterior lip of the vesicle 

 is directly continuous with the cephalic lobes. 



The openings of the lateral invaginations are no longer to be seen 

 in surface views. Sections show that vesicles have been formed by 

 these invaginations which lie beneath the lateral margins of the optic 

 lobes, each vesicle possessing a lumen of considerable size. 



The cerebral lobes have continued to increase in thickness, partly 

 by a continued increase in the number of their cells, and partly by 

 the crowding of the neural elements of the lobes into a more compact 

 mass. 



The shifting of the neuromeres has placed the two halves of the 

 cheliceral segment laterally to the stomodteum which is now a deep 

 invagination of the ectodenn covered by a fiat, triangular rostrum. 

 The lateral eyes first appear as thickenings of the ectoderm (I. c.) at 

 a point on the margin of the cephalic plate somewhat posterior to 

 the position of the lateral vesicles. 



Immediately below the rostrum a small depression is to be seen in 

 the ectoderm which bridges the longitudinal furrow (c. p.). Patten 

 found a chain of such pits between the segmental neuromeres of the 

 scorpion, and related them to the "'mittelstrang" of Hatscheck. 

 According to Patten, this chain of pits gives rise to the bothroidal 

 cord. In Epeira, however, I have been unable to discover more than 

 the single pit. 



A transverse section made through the region of the stomodaeum 

 shows that structure to be flanked on either side by a lateral ganglion 

 of considerable size. These ganglia arose in connection with the 

 cheliceral segment, and they are now connected by a strand of nerve 

 tissue which passes from one to the other beneath the stomodaeum 

 (s. s. c). These ganglia, at a later period, become fused with the 

 main portion of the brain, the connecting strands of nerve tissue 

 forming the sul)-stomoda'al connectives which are present in the adult 

 brain of the spider (St. Remy, 39). 



Stage VIII. Fig. 28. — This stage shows many features of advance 

 in the morphology of the cephalic plate. The cephalic fold has grown 

 until it covers a little more than the anterior third of the brain (o. /.). 



