SENSOKY AKE REPRODUCTIVE ORG-ANS. 193 



nating with the dorsal nerves ; a ventral nerve 

 on one side being opposite a dorsal nerve on the 

 other. Each arises by a large number, thirty or 

 more, of very slender rootlets, placed one in front 

 of another, the entire breadth of a ventral root 

 being nearly equal to the interval between two 

 successive roots. The several rootlets do not 

 unite, but pass separately through the connective- 

 tissue sheath of the cord, and end in the myo- 

 tomes. 



L. The Sense Organs. 



The sense organs of Amphioxus are extremely simple in 

 structure, and differ markedly from those of the higher verte- 

 brates in being unpaired. 



1. The pit-like depression of the skin which in the young 



places the central canal of the nervous system in 

 communication with the exterior has been described 

 as an olfactory organ. In the adult it is connected 

 by a solid stalk with the roof of the ventricle. 



2. The ' eye ' is a rounded pigment-spot in the anterior wall 



of the ventricle, i.e. at the extreme anterior end of 

 the central nervous system. 



M. The Reproductive Organs. 



Th^ , s^es are distinct, but the males and females are 

 alike except as regards the microscopic structure of their 

 reproductive organs. There are no genital ducts. 



1, The female. 



The ovaries are a series of saccular organs of a 

 horseshoe shape, arranged in a row along the inner 

 surface of the atrial fold on each side of the pharynx, 

 and extending back as far as the atrial pore. They 

 lie in cavities, which are extensions of the coelominto 

 the atrial folds ; these cavities are easily recognis- 

 able while the ovaries are young, but become almost 

 obliterated when the ova ripen. 



The ova, when mature, are discharged into the 







