TRACHEATA. 



431 



(428) Tichomiroff. " Ueber die Entwicklungsgeschichte des Seidenwiirms." 

 Zoologischer Anzeiger, n. Jahr. No. 20 (Preliminary Notice). 



(429) Aug. Weismann. "Zur Embryologie d. Insecten." Archiv f. Anat. 

 und Phys. 1864. 



(430) Aug. Weismann. " Entwicklung d. Dipteren." Zeit. f. wiss. Zool. 

 Vols. xin. and xiv. Leipzig, 1863 4. 



(431) Aug. Weismann. " Die Metamorphose d. Corethra plumicornis. " Zeit. 

 f. wiss. Zool. Vol. xvi. 1866. 



(432) N. Wagner. "Beitrag z. Lehre d. Fortpflanzung d. Insectenlarven." 

 Zeit.f. wiss. Zool. Vol. xin. 1860. 



(433) Zaddach. Untersuchungen iib. d. Bau u. d. Entwicklungd. Gliederthiere. 

 Berlin, 1854. 



ARACHNIDA 1 . 



The development of several divisions of this interesting 

 group has been worked out ; and it will be convenient to deal in 

 the first instance with the special history of each of these 

 divisions, and then to treat in a 

 separate section the develop- 

 ment of the organs for the 

 whole group. 



Scorpionidae. The embry- 

 onic development always takes 

 place within the female Scor- 

 pion. In Buthus it takes place 

 within follicle-like protuber- 

 ances of the wall of the ovary. 

 In Scorpio also development 

 commences while the egg is 

 still in the follicle, but when the 

 trunk becomes segmented the 

 embryo passes into the ovarian 

 tube. The chief authority for 

 the development of the Scorpio- 

 nidae is Metschnikoff (No. 434). 



At the pole of the ovum facing the ovarian tube there is 



FIG. 193. OVUM OF SCORPION WITH 

 THE ALREADY -FORMED BLASTODERM 

 SHEWING THE PARTIAL SEGMENTATION. 

 (After Metschnikoff.) 



bl. blastoderm. 



1 The classification of the Arachnida adopted in the present work is shewn below. 

 c Scorpionidse. . . ( Tetrapneumones. 



Pedipalpi. IL Aranema - JDipneumones. 



I. ArthrOgastra. \ Pseudoscorpionidae. 



I Soiifugse. in. Acarina, 



^ Phalangidse. 



