NOTES ON THE DEVELOPMENT OF THE ARANEINA. 93 



ganglionic thickening for the chelicerce quite independent of 

 the procephalic lobes. 



In the procephalic lobes the epiblast is much thickened, 

 and is formed of several rows of cells. The greater part of 

 it is destined to give rise to the supra-uesophageal ganglia. 



During the various changes which have been described the 

 blastoderm cells have been continually dividing^ and, together 

 with their nuclei, have become considerably smaller than at 

 first. The yolk cells have in the meantime remained much 

 as before, and are, therefore, considerably larger than the 

 nuclei of the blastoderm cells. They are more numerous 

 than in the earlier stages, but are still surrounded by a 

 protoplasmic body, which is continued into a protoplasmic 

 reticulum. The yolk is still divided up into polygonal seg- 

 ments, but from sections it would appear that the nuclei are 

 more numerous than the segments, though I have failed to 

 arrive at quite definite conclusions on this point. 



As development proceeds the appendages grow longer and 

 gradually bend inwards. They become very soon divided by 

 a series of ring-like constrictions which constitute the first 

 indications of the future joints (PI. VII', fig. 6). The full 

 number of joints are not at once reached, but in the ambu- 

 latory appendages five only appear at first to be formed. 

 There are four joints in the pedipalpi, while the chelicerae do 

 not exhibit any signs of becoming jointed till somewhat later. 

 The primitive presence of only five joints in the ambulatory 

 appendages is interesting, as this number is permanent in 

 Insects and in Peripatus. 



The next stage figured forms the last of the third 

 period (PI. VIII, fig. 7 and la). The ventral plate 

 is still rolled round the egg (fig. 7), and the end of the tail 

 and the procephalic lobes nearly meet dorsally, so that there 

 is but a very slight development of the dorsal region. There 

 are the same number of segments as before, and the chief 

 difierences in appearance between the present and the 

 previous stage depend upon the fact (1) that the median 

 ventral integument between the nerve ganglia has become 

 wider, and at the same time thinner ; (2) that the limbs have 

 become much more developed; (3) that the stomodaeum is 

 definitely established ; (4) that the procephalic lobes have 

 undergone considerable development. 



Of these features, the three last require a fuller descrip- 

 tion. The limbs of the two sides are directed towards each 

 other, and nearly meet in the ventral line. The cheliceree 

 are two-joipted, and terminate in what appear like rudi- 

 mentary chela?, a fact which perhaps indicates that the 



