76 



K. KTSHINOYUE. 



parts stanrling apart as heretofore. The transverse bar (fiof. 44, a) of 

 the T-shaped brain is separated from the median stem just behind 

 the point where the Inmina of the two sides communicate with each 

 other, while the median stem is in its turn transversely divided into 

 two segments (Fig. 44. b, e). Thus the spider's brain consists of 

 three segments, as l^ntten* claims. These three segments may be 

 called the transverse dorsal (Fig. 44, a), the anterior ver.tical (Fig. 44, 

 />), and the posterior ventral section (Fig. 44, c). The lateral vesicles 

 arein the level ofthe third segment. From his description. Patten seems 

 to mean that in scorpions and spiders the three segments (^f the brain 

 are formed from three separate invaginations ; but I cannot cor- 

 rol)ornte this statement. Moreo^er he says that the anterior median 

 eyes (my posterior median eyes) belong to the second segment, while 

 the three remaining pairs belong to the third segment. Supposing 

 tlint his second segment is anterior to the third segment, 1 cannot 

 corroborate this statement either, as accoixling to my own ol)servati<^ns 

 all the eyes belong to the third segment. It seems to me impossible 

 tliat the posterior eyes should arise in a segment anterior to that in 

 whicli the anterior eyes are produced. 



The opening of the sacs of the posterior median eyes becc^mes 

 gradually smaller and is finally closed (PI. XYI, fig. 49). The 

 anterior wall ofthe sac becomes enormously thick and obliterates its 

 lumen. The ectodermic cells which lie ii])on the sac elongate and 

 form the vitreous body (tigs. 49, 54, ivV). The anterior wall of the 

 sac forms the retinal part (fig. 49, PC). The retinal cells elongate 

 anteriorly. The anterior surface of the anterior wall of the posterior 

 median eyes, is morphologically the inner side of the ectoderm 

 though it faces externally. The lens is formed by a local thickening 

 of rhe cuticula, which is secreted from the epithelium at this stage 



* Patten — Segmental Sense-organs of Arthropods, Journ. of Morph. II. ^ 



