Development of the Spiders. 209 



two pairs ; the third smaller pair is not formed until later. 

 The spinnerets at first occupy a much larger space than 

 they afterwards do ; subsequently they become more concen- 

 trated and rise into small and more definitely circumscribed 

 m ami Ike. 



III. The young Spider. 



The passage from the embryonic band to the young spider 

 rolled up in the egg is therefore much more complex than as 

 described by Claparede. It is during its progress that all the 

 most essential phenomena of the internal development take 

 place ; and it consists, as we have seen, of two great periods — 

 the passage from the embryonic band to the Limuloid stage, 

 and the passage from the Limuloid stage to the young spider. 

 When this last stage is arrived at, the spider is constituted 

 in all its most essential points, and already presents its defini- 

 tive form. We can obtain a sufficiently good idea of the sub- 

 sequent developmental aspects by consulting the figures given 

 by Herold, who carefully studied this period. The most 

 important phenomenon which occurs during it is the formation 

 of the inner lamella, which is produced at the expense of the 

 nutritive vitellus. Up to this time the vitelline masses retain 

 an irregular arrangement. This irregularity persists in the 

 masses of the centre, but ceases in those of the surface, which 

 acquire a very regular arrangement at the period of the 

 extension of the tergal plate. At the same time there appear 

 between their boundaries trains of opaque granules ; these 

 trains rapidly increase in thickness, and soon present from 

 place to place white spots recognizable as nuclei. These 

 nuclei increase simultaneously with the granules. The latter 

 represent the protoplasm, and speedily collect around the 

 nuclei to form cells, which then begin rapidly to multiply and 

 soon clothe the whole surface of the vitellus. 



This appearance of the inner lamella is not without analogy 

 with that of the blastoderm ; and it would appear that, as 

 Bobretzky has already indicated in Palcemon and Omscus, the 

 vitelline mass is twice active — once to form the outer lamella, 

 and a second time to form the inner lamella. I do not think 

 that we have here an immigration of blastodermic cells into the 

 interior of the mass of the nutritive vitellus : I have never 

 seen any thing that would justify such an assumption ; and I 

 rather incline to believe that the productive activity of the 

 vitelline mass is not exhausted by the formation of the 

 blastoderm, and that there remains in it sufficient to pro- 

 duce the nuclei which we see reappear in the trains of pro- 

 toplasm. 



