in the center of the spot is related. Thus, Pander distin- 

 guished two parts in the cicatrice — the disk, or membranous 

 layer, and the central lump situated below it, to which he 

 gave the name nucleus^ f the cicatrice. Pander gave great 

 consideration to the membranous layer and called it the 

 blastoderm (67) . 



At the eighth hour of incubation (§2) C68) the 

 nucleus of the disk is more easily separated from the yolk, 

 but it remains attached to the blastoderm. The latter 

 increases insignificantly in size, its center somewhat 

 clarified. 



The twelfth hour of incubation (§ 3) is character- 

 ized by further spreading of the blastoderm; its trans- 

 parent central part also increases and changes the round 

 form into a pear-shaped form. In the blastoderm at that 

 time it is possible to differentiate two regions: the 

 internal region called the transparent area (area pellucida) 

 (69) , surrounded by a non-transparent region, called "the 

 opaque area" (area opaca) . Through the transparent area 

 the nucleus of the cicatrice is visible, "giving Malpighi 

 a reason for his strange mistake and imaginary picture e "17 

 "The greatest importance," Pander wrote, "is that the 

 blastoderm itself is composed of two layers. This membrane 

 before incubation consists of a single layer of granules. 

 In the process of incubation the second very thin layer 

 appears* however, it is so firm that by prolonged maceration 

 it is possible to separate the blastoderm into two layers." 

 (70) "The internal of these layers," Pander continued, "is 

 connected with the yolk. We will call it later the mucous 

 membrane, and the external homogenous and smooth layer the 

 serous membrane. Both these membranes spread over all the 

 blastoderm and are present in the transparent as well as in 

 the opaque area, with only the difference that in the 

 transparent area the mucous membrane is much more delicate 

 than in the opaque area. "18 



16. Called "Pander's nucleus" by subsequent authors, 



17. Pander, DISSERT AT 10, p. 25. 



18. Ibid., p. 27. 



246 



