8 



K. MITSUKUR1. 



end of the latter month larger individuals have finished shedding their 

 reproductive elements and retired into their summer shelter, while the 

 younger ones (the second year ones) are just ending their spawning. 



The duration of the breeding season may be graphically shown by 

 the following diagram : — 



Jan. 



Feb. 



Mar. 



Apr. 



May 



June 



July 



Aug. 



Sept. 



Oct. 



Nov. 



Dec. 



m 





■ ■■1 



11^ 



















The diagram needs no explanation after what has been said above. 

 The dots in Jan. Feb. Mar. and April show irregular or very early 

 cases of jipcned reproductive elements which may be shed out of 

 season. The height of the season is from the middle of May to the 

 middle of July. 



The reproductive glands at the height of the breeding season are 

 a very conspicuous organ in the body cavity. As soon as a cut is 

 made in the skin, the ends of the branches begin to ooze out : they 

 form an immense mass among the viscera. (One of the reproductive 

 tubes with all its branches laid in one single straight line attains at 

 this time the length equal generally to that of the body itself or even 

 more. In Fig. I is shown an ovarian tube and in Fig. 2 a spermatic 

 tube, each with all its branches. It will be seen that a tube divides 

 clichotomously several successive times, the whole assuming a dendritic 

 shape. It will also be seen that the male tube is peculiarly nodose. 

 This is produced by the spermatic fluid specially collecting at different 

 points and producing swellings. When one of these tubes is left in 

 water one hour or so, the nodes become much more conspicuous owing 

 to the fresh local accumulations of spermatozoa or the spermatic fluid. 

 The ovarian tube has a transparent red (a light shade of burnt sienna), 

 and the spermatic the white color. There are about ten of these 

 branching tubes hanging down from each side of the dorsal mesentery. 



