THE EMBRYOLOGY OP A SCOEPION. 129 



Stage M. — The changes from the last stage up to the time 

 of hatching are not very numerous, though very important. 

 The body attains a structure almost exactly like that of the 

 adult, the appendages being segmented and the whole animal 

 covered by a thin, structureless, highly refracting cuticle. The 

 coxal gland still opens by a small aperture to the exterior at 

 the base of the fifth appendage (PI. XVIII, fig. 54). This 

 aperture, which is lined for a short distance by the cuticle, 

 leads to a straight duct (fig. 54) lined by cubical cells with 

 round nuclei, which closely resemble the cells of the gland. 

 The gland itself is distinguishable into medullary and cortical 

 portions as described by Professor Lankester^ in the adult. The 

 tubules have distinct lumens surrounded by acubical epithelium. 

 The gland and its duct are surrounded by a thin capsule of flat 

 mesoblast cells. 



The genital tubes have pushed their way some distance 

 between the lobes of the liver, but they are not yet connected 

 by transverse tubes nor do they open to the exterior. The two 

 layers of which the tube is composed in the adult (v. supra, 

 p. 108) are not yet distinguishable. The pectines approximate 

 very closely to their adult structure. 



The ninth, tenth, eleventh, and twelfth appendages are also 

 very similar to those in the adult (PI. XVIII, fig. 55). The 

 number of lamellse is not so great, but their structure is very 

 well shown. Each lamella is covered by a thin cuticle, and its 

 cavity is in direct communication with a blood-sinus (fig. 55, 

 bl. s.). The cells which form the lamellse are very large, espe- 

 cially towards the base of the appendage. Towards the apex 

 they become smaller, and finally pass into a mass of different 

 cells from which more lamellse are formed as the animal grows. 

 The spaces between the lamellse (fig. 55, a. c'.) are narrower and 

 in communication with the exterior through the stigma. 



The head is now completely formed, the mouth having 

 shifted so as to lie behind the chelicerse. The invagination 

 which forms the central eyes has closed up. A stage immedi- 

 ately after its closure is shown in PI. XVIII, fig. 56. Here the 

 > ' Proc. Roy. Soc.,' vol, xxxiv, 1882-83, 



