132 



CHIM-€ROID FISnKS AND THEIR DEVELOrMENT. 



embryologically at least, indicate a primitive sei^Miiented condition (Redecke), and 

 I am led to suggest that the "segmentation" of the kidney of the adult arose 

 secondarily. The absence of the Geschlechtsniere in Chimseroids, moreover, I also 

 interpret as a secondary reduction, an accompaniment of the enormous develop- 

 ment of kidney in a short body cavity, a process which caused an enlargement of 

 functional nephric tubules, an obliteration of rudimentary ones, and more direct 

 and special means of carrying out gonadial jiroducts. In favor of the last inter- 

 pretation are the great size and elaborate regional differentiation of Wolthan and 

 Miillerian ducts. 



NERVOUS SYSTEM. 



The following features in the development of the system may be mentioned as 

 indicating that the Chima^roids have been subject to wider changes than kindred 



sharks. 



Reduction of Cord. — The cord in the region of tail and hinder trunk, repre- 

 senting about 60 per cent of its entire length, is greatly modified. Contrast in this 

 region the diameter of the cord, its histological differentiation, the size, number, 

 and character of the roots of the spinal nerves. The flattening of the cord in the 

 hinder trunk and tail region is, therefore, hardly to be compared to the condition 

 in Cyclostomes. 



Jdcxiirc of Jh-aiii. — In Callorhynchus icf. Schauinsland's Taf. xxii) the brain 

 shows extraordinary ffexures; in the region of the midbrain its axis changes direc- 

 tion by almost 180°. 



Size of IiifiuidibuliDii. — In early stages the infundibulum attains great size; 

 and concomitantly the dorsal wall of the diencephalon is compressed between the 

 forebrain and the optic lobes. 



Separation of Ilcniisplicrcs. — In this regard the early condition is more marked 

 than in any other fish-like vertebrate. Ob.serve also the separation of the entire 

 forebrain fr(.)m the midbrain. This in Chima'ra begins in early stages and in the 

 adult attains remarkable j^roportions. 



