History of a transient nervous apparatus in certain Ichthyopsida. 375 



the process of breaking-up. The withered remains of capsule-cells 

 (cc) are still evident (Figs. 120—121). The degeneration is now 

 going on far more rapidly. 



14. Embryos of 19 cm (Nos. 322, 323). 



The length is made up as follows : — from snout to end of pelvic 

 fins 8 cm, and thence to end of tail 11 cm. Across the widest part 

 of the pectoral fins the embryo measures 8,7 cm. The embryo is 13 

 to 14 months old. 



The figures from embryo No. 322 are Figs. 124 and 129 a— d, 

 plate 29, and from embryo No. 323, Figs. 122, 123 and 128 on the 

 same plate. 



The degeneration has advanced by leaps and bounds^). The 

 reader will readily admit that the figures of both embryos prove this. 

 The cells have lost entirely everything that stamped them as ganglionic 

 in nature. The regular shape has given place to a most irregular 

 jagged elongated form. They are nothing but the ragged remains of 

 cells. Shrunk and withered in appearance, but here and there with 

 remains of former processes (Fig. 129 b n.p). The nucleus varies in 

 appearance. Sometimes it is more apparent than at others, its usual 

 form is that of a seemingly empty bag, and only occasionally can 

 the remains of nucleoli be detected. The nucleus, again, stains but 

 faintly, no longer possessing any affinity for colouring matters. Remains 

 of capsule cells (Figs. 122, 123 cc) still meet the eye. 



15. Embryo a month older than No. 322. 

 Embryo No. 336 was preserved 31 days later. It is not distin- 

 guished by its length; because, as a matter of fact, it measures only 

 18 cm 2). But, that it is older than the preceding two is proved by 

 its greater width, i. e., across the fins 10,25 cm. The length of the 

 body is the same as in No. 322, viz. 8 cm. There are no traces of 

 external gills. 



1) There are in the collection no embryos of stages between 16 cm 

 and 19 cm. Had it been anticipated that the degeneration would have 

 proceeded so slowly such intermediate stages might have been secured. 

 When these advanced embryos were alive, there was no time available 

 for investigation, and thus the steps taken to secure proper material 

 had to be by gropings in the dark. 



2) The greatest length ever attained by embryos of R. batis within 

 the purse probably does not exceed 19 cm. There is then perhaps a 

 slight absorption of the tail-end. This appears to have been noted by 

 J. Müller in his memoir "Ueber den glatten Hai etc." previously cited. 



