412 JOHN BEARD, 



9 mm, in which other organs of the animal are only iu their very 

 beginnings; it persists intact, until the embryo is upwards of 43 mm 

 in length, and about then reaches its culmination. Degeneration does 

 not as a rule set in, however, until the embryo attains a length of 

 nearly 70 mm. 



The period of functional activity appears to be a prolonged one 

 in Raja batis^ far longer than in any other form yet investigated. 

 In other forms its life-period may be represented by weeks, or even 

 by days, instead of by months. 



In Raja hatis it remains quite normal for two months or longer 

 of the 17 months of the embryonic development within the egg-capsule. 

 Then it enters upon the long slow path leading to complete degener- 

 ation, the end of which is reached in 12 months or more. 



The degeneration of the various elements is described in detail 

 in the paper. Apart from odd members of the vagrant ganglion-cells 

 the nerves appear to be the first to die. Their degeneration is fol- 

 lowed by a slow atrophy of the ganglion-cells, and in fact, as indicated 

 in the Lepidosteus paper ^) and now extended to include the nerves, 

 the whole series of changes undergone by these cells corresponds 

 exactly to that degeneration and death of nerve-cells and nerve-fibres 

 which the pathologists term "simple atrophy". This occurs normally 

 in every embryo, and in the paper the histological changes are illu- 

 strated and described in some detail. 



After a section devoted to a discussion of the mode of nerve- 

 development in the transient apparatus , a few lines are assigned to 

 the description of a process termed "degradation of ganglion-cells". 

 "By degradation of ganglion - cells is meant the losing of specific 

 ganglionic characters and functions, when a cell, whose phylogenetic 

 history is ganglionic, sinks to the position of a mere nucleus in the 

 conducting fibre to which it has given origin." 



Another section is given over to "preliminary remarks on per- 

 manent giant ganglion-cells" in other forms, including those of Am- 

 phioxus. Against the views of others it is urged that in older Raja 

 and Scyllium embryos ganglion-cells occur which are perhaps the 

 homologues of those of AmpMoxus, and several decisive objections 

 are stated to von Kupffer's attempts to seek equivalents to the 

 transient nerves in the posterior nerve-roots of Amphioxus. 



Still further on it is pointed out that, even at its prime, the 



1) op. cit. p. 117. 



