Development of the Spiders. 201 



at this stage the ventral pads do not tend to become effaced, 

 as Claparede says, but that, on the contrary, they are in a 

 progressive course ; we see, moreover, that the formation of 

 appendages is not irregular and variable according to the 

 species, but that it is constantly limited to the first four 

 zonites. 



II. Limuloid Stage. 



According to Claparede, the whole passage from the state of 

 embryonic band to that of the young spider rolled up in the 

 egg is reduced to a translation of the ventral pads towards the 

 dorsal region ; this displacement in its turn causes an approxi- 

 mation towards the ventral region of the two extremities of 

 the embryo, and thus produces its rolling up in proportion as 

 the ventral pads separate from each other. The nutritive 

 vitellus protrudes through the fissure which these pads have 

 left between them (fente sternale, Clap.), and finally passes 

 entirely through this fissure, so as to become completely ven- 

 tral : the position of the embryo is thus entirely changed ; and 

 it becomes rolled in the opposite direction to its former one. 



This process is completed at the period when the ventral 

 pads have come to occupy the lateral epimeral region, of which, 

 according to Claparede, they are the representatives (we have 

 seen that this interpretation is erroneous, and that they repre- 

 sent in addition the sternal and tergal arcs, the part occupied 

 by the limb alone really forming the lateral region). Their 

 presence at this point keeps the two faces of the embryo dis- 

 tinct for a moment ; but they soon finally disappear, so that 

 we no longer distinguish one face from the other, and the 

 posterior part of the body assumes the globular form so cha- 

 racteristic of the abdomen in the adult. 



The passage of the vitellus through the sternal fissure is a 

 unique fact in the group Arthropoda ; and the interpretation of 

 it given by Claparede makes something quite peculiar out of 

 the embryogeny of the Spiders. Ingenious as this conception 

 may be, however, it is far from sufficing to explain the passage 

 from the embryonic band to the state of the young spider 

 rolled up in the egg, and one feels the necessity of a less 

 theoretical description. 



In order to trace this passage in all its details, we shall take 

 up again the last stage of the germinative band and examine 

 its changes step by step ; the phenomena differ according as 

 we examine the anterior, middle, or posterior portion of the 

 body. 



1. Anterior portion. — The buccal depression becomes -in- 

 vaginated, and gives origin to a tube ; the latter, which grows 



