xvi DEVELOPMENT 435 



within themselves, they develop a temporary stomach and a 

 large sucking organ, and become for a time independent sucking 

 animals, imbibing the fluids in the common sac, and arranged 

 around its circumference with their mouths directed towards the 

 centre.- Subsequently a second embryonic stage is entered upon, 

 the sucking organ being discarded, and the albuminous matter 

 which the larva has imbibed being treated anew like the original 

 yolk of the egg. 



It is an interesting fact that in this second embryonic stage a 

 well-marked " tail" or post-abdomen is formed, and the ganglionic 

 nerve-masses increase in number, a cerebral mass being followed 

 by eight pairs of ganglia in the body and eight in the tail. 



A B 



FIG. 224. Three stages in the development of Chelifer. 



A, Segmenting ovum ; B, embryo, with post-abdomen, maximum number of ganglia, 

 and developing sucking apparatus ; C, larva. (After Barrois.) 



Subsequently a great concentration takes place till, besides the 

 cerebral mass, only five closely-applied pairs of ganglia remain, 

 corresponding to the pedipalpi and the four pairs of legs. More- 

 over, the first pair advances, so as to lie on the sides of, and not 

 behind, the oesophagus. 



There are two ecdyses or moults during development, a partial 

 moult, concerning only the ventral surface of the " pro-embryo " 

 as it assumes the larval form, and a complete moult at the final 

 stage, before emergence from the incubating sac. 



At the end of winter the mother cuts a hole in the silken 

 web, and the young brood issues forth. 1 



1 For the embryology of Chernetidea, see J. Barrois, "Mem. sur le developpement 

 des Chelifers," Rev. Suisse de Zool. iii., 1896. Metschnikoff, Zeitschr. wiss. Zool. 

 xxi., 1876, p. 514 ; and Vejdovsky, Congres zool. international de Moscou, 1892, 

 p. 120, may also be consulted. 



