220 



KINGSLE Y. [ Vol. \' 1 1 1 . 



gradually shifts its position backward." Kishinoiiye has nothing 

 to offer concerning mesenteron or proctodaeum. 



In the Arachnida almost all observers describe conditions 

 closely similar to those obtaining in Limulus. Since the time 

 of Balfour's paper ('80) the liver-lobes have been recognized as 

 differentiated by the ingrowth of mesodermal septa into the 

 yolk in the same manner as in Limulus, and the hepatic ducts 

 (of course different in number) as formed in substantially 

 the same way. Balfour, while thinking that certain obser- 

 vations possibly pointed to the origin of the hepatic epithelium 

 from the cells of the thickened ends of the septa, still recog- 

 nized the entoderm in the yolk. Balfour did not trace the 

 formation of the entodermal epithelium but later authors agree 

 that it arises in the spiders from the yolk cells, the differenti- 

 ation beginning at first at the posterior end. So far as their 

 observations go Locy, Morin (the text of his preliminary paper, 

 the copies of the figures of his later article in Russian), and 

 Schimkewitsch ('87) agree in the recognition of the yolk nuclei 

 of spiders as the nuclei of the future entoderm. Later, Schim- 

 kewitsch ('90) changes his views ; he now recognizes as ento- 

 derm in the " Tracheates," the smaller cells which lie on the 

 ventral surface of the yolk, while the mass of the yolk cells in 

 the Arachnids are the Anlage of the blood corpuscles. Such a 

 view is impossible with Limulus, since before the yolk cells 

 undergo any change they are entirely enclosed in the splanchno- 

 pleural layer of the mesoderm, through which migration to 

 the blood vessels is impossible. 



Faussek, in his account of the development of the Phalangids 

 (•91) says that at the close of the embryonic period the yolk 

 cells (derived as in Limulus by delamination) divide rapidly, 

 and, with a small amount of protoplasm, begin to throw them- 

 selves down upon the mesodermal envelope of the midgut and 

 its diverticula. At first these patches of entodermal epithelium 

 are irregularly scattered but they soon begin at the anterior 

 end, to arrange themselves in the cylindrical epithelium of this 

 region. 



In the scorpions the conditions are quite different. As 

 already pointed out (Vol. VII, pp. 55 ff.) Kowalevsky and 



