364 Maximilian Herzog. 



teen outline drawings on 2 mm. wax plates prepared by Selenka, 

 and found after his death. Nothing is reported concerning the 

 model except the following.* 



"Neither an allantoic duct nor an amniotic duct was found. 

 The external surface of the yolk sac appeared uneven (hockerig), 

 as if the 'anlagen' of vessels and blood had already been formed, 

 but naturally this point could not be definitely decided from the 

 wax plates and the model." 



After Peters' ovum, the next youngest embryo enumerated by 

 Keibel and Elze in the ''ISTormentafeln" is the one described by 

 von Spee in 1896. It had a longest diameter of 1.84 mm., and a 

 longest yolk sac diameter of 1.054 mm. Length of amnion and 

 allantoic stalk, 0.76 mm. ; greatest width of the two latter, 0.76 mm. ; 

 greatest width of yolk sac, 1.083 mm. ; length of embryonic 

 shield, 0.37 mm.; width of ectoblast plate, 0.23 mm.; length of 

 allantoic duct, 0.35 mm. No amniotic duct was present. Between 

 mesoblast and entoblast there were blood islands which caused the 

 mesoblast to project strongly. 



The authors of the "Normentafeln" believe that the embryo 1.74 

 mm. long described by Beneke, is older than von Spec's embryo. 

 They consider that the description of Beneke's specimen is unsatis- 

 factory. 



The Frassi embryo, the youngest examined in compiling the tables 

 which accompany the "Normentafeln," is described as follows: 

 Length of embryonic shield, 1.17 mm.; width, 0.6 mm.; diameters 

 of yolk sac, largest, 1.9 mm. ; smallest, 0.9 mm. The embryonic 

 shield is flat, with a long primitive streak (0.5 mm.) and a shallow 

 medullary groove. The medullary folds are not yet sharply defined 

 At the anterior end of the primitive streak the canalis neurentericus 

 is indicated (whether it is pervious is questionable) ; at the posterior 

 end is the "anlage" of the cloacal membrane. There are no myo- 

 tomes. "Anlagen" of vessels and blood are found on the yolk sac, 

 and there are vessels in the allantoic stalk and adjacent chorion. 

 There are no vessels in the embryonic shield. The amnion is 



*Keibel and Elze, Vol. 8 of Keibel's Normentafeln zur Eiitwicklimgsgesch. 

 d. Wirbelth., 1908, p. 9. 



