12: 



li. NAKAGAWA. 



presently bo stated. The ova and the spermatozoa, however, are not 

 yet fully ripe, for when these are subjected to examination the former 

 are not separable from one another and the latter not uniformly 

 developed. From these observations, it is quite «evident that the period 

 of active egg-làying must be between the middle of June and the end of 

 July. The relation of the size of the animal to its sexual maturity, I 

 have already stated above. 



The color of the gonads is orange-red in the female and pale yellow 

 in the male. 



V. The Number of Buccal Cirri and Branchial Archen. 



• 



The buccal cirri were counted under the microscope by cutting out 

 the margin of the oral aperture completely around and placing the cut- 

 out part under a cover glass. To make out the branchial arches, the 

 left side of the pharyngeal wall was dissected off and examined under the 

 microscope. The results are given in the following table. 



TABLE III. 



Body length. 



Total number 

 ol segments. 



Xo.of hranch, 



arches on 

 the leftside. 



No. of cirri 



on the 

 right side. 



Median 

 cirrus. 



No. of cirri 



on the 

 right side. 



46 "È 



... 64 ... 



.213 It. 



... 19 ... 



... 1 ... 



... 20 





... 64 ... 



...183 ... 



... 20 ... 



... 1 ... 



f-... 20 



28£... 



... 63 ... 



...137 ... 



... 20 ... 



... 1 ... 



... 20 



26 ... 



... 64 ... 



...121 ... 



... 20 ... 



... 1 ... 



... 20 



The number of the buccal cirri is thus nearly constant — i. e. 20 on 

 each side, but the number of the branchial arches varies, increasing with 

 the growth of the body, as suggested by Bateson.* 



* Bateson— Materials for the Study of Variation, p. 174, foot-note. 



