ON THE DEVELOPMENT OF ARANEINA. 75 



dages become rounded in outline (PI. XV. figs. 35, 36). They are 

 easily distinguished from the fat eells by their centrally located 

 nuclei, and from other cells by their well-defined spherical form and 

 slightly stninable protoplasm. They appear first in the chelicenv, 

 then in the pedipalpi, nnd so on gradually backwards. These cells 

 liave no relation whatever with the coxal gland uov with the poison 

 gland. Their function is unknown. It seems to me that Locy has 

 mistaken these cells at the base of the chelicera^ for the first rudi- 

 ments of the ])oison gland. He says that these cells are probably 

 derived from an infolding of the ectoderm. 



From the End of the Reversion to the Hatching 

 of the Embryo. 



This stage is characterized by the api)earance of a constriction 

 separatiiig the céphalothorax from the abdomen. The yolk in the 

 ventral part of the abdomen is absorbed, so that the abdominal 

 appendages of both sides appr("»ach each other at the median line. 



The senncircular grooves of the cephalic lobes formed in the 

 preceeding stage are no longer grooves, nor semicircular in form. 

 Now they are completely constricted oif from the general ectoderm, and 

 are consequently tubes. Their inner Yunhs approach each other in the 

 median line and they form as a whole a T-shaped body (PI. XV, fig. 

 45). The lumina of the two tubes communicate with one another at 

 the anterior median part. They as well as the lumen of the lateral 

 vesicle begin to atrophy by the thickening of their walls and finally 

 disappear. At the same time the transverse bar of the T-shaped 

 mass becomes curved on each side to a peculiar shape shewn in 

 profile in fig. 45 a. This and the disappearance of the lumen change 

 the brain into a compactly packed mass, instead of having its various 



