History of a transient nervous apparatus in certain Iclithyop^iiln. 37H 



Figs. 108 a and 108b are from embryo No. 285. The cells ar>' 

 seen to be in much the same condition as those in Figs. 1"'J and 

 110, but the remains of processes are not so evident, and only oiu; 

 nucleolus can be made out in each cell. lu connection with the 

 ganglion-cells in both of these embryos it should be added that 

 remains of capsule- cells, also in a starved condition, can be detected. 



11. Embryo of 12,5 cm. 



Embryo No. 263 is a female. The body from the rostrum to 

 the end of the pelvic fins measures 4,25 cm, and the length of the 

 tail is 8 cm. The greatest width of the body across the pectoral 

 fins is barely 4 cm. The external gills are in process of absorption 

 and are only some 5 mm long. It may also be noted that the for- 

 mation of the permanent central canal of the cord in the anterior trunk- 

 region is approximately complete. The embryo is about l^j.^ months 

 old. Figures from this embryo are Fig. 33, plate 23, and Figs. 112 

 and 112 a, plate 28. 



As revealed by the two latter figures , which are from sections 

 in the region of the thymus ^), in this embryo the ganglion-cells are 

 not so deeply wedged into the posterior fissure, and hence they retain 

 to some extent their original shape. In the present embryo they 

 do not appear to be in so degenerated a state as in the two previous 

 ones. Thus it may be suspected that the rate of de- 

 generation varies in different embryos. The size of the 

 processes, as far as can be seen, is smaller, but the nucleus appears 

 to have undergone but little shrinkage. 



The other figure (Fig. 33, plate 23) will be referred to sub- 

 sequently in another connection; it is intended to show a ganglion- 

 cell if.gl.c) stretching across the posterior fissure. 



12. Embryos of 14 cm. 



Embryo No. 294 is a male. The body measures from the rostrum 

 to the end of the claspers 5 cm, and the length of the tail from this 

 point is 9 cm. The greatest width from side to side is 5,25 cm. 

 The external gills are almost absorbed and are now only 1 mm long. 

 The embryo is about 9 months old. 



1) Experience teaches one that in the stages of degeneration the 

 transient ganglion-cells are to be met with in greatest abundance in 

 Raja in that portion of the trunk which extends from the posterior 

 part of the thymus to the beginning of the genital organs. 



25* 



