438 NAOHIDE YATSU 



nature is usually found there. The cytoplasm of the yellow 

 gland cell is fibrillar, in contrast to that of mucous cells, which 

 is granular as has already been mentioned. Figure 4 shows a 

 section through the anterior protuberance near the openings. 

 Here we see very clearly the relative position of both kinds of 

 gland cells. 



In comparison with Cypridina hilgendorfii, the maxillary gland 

 of Pyrocypris japonica (Miiller '90, p. 233^ Was studied. The 

 protuberances of the latter differ both in shape and number from 

 those of the former, one unpaired one being added in front. 

 But so far as the internal make-up of the glands is concerned, 

 it is so similar that its description would be simply the repe- 

 tition of what has been stated above. The only difference is the 

 presence of pigment cells in the upper hp of P. japonica. 



In conclusion, I would like to emphasize once more the two 

 points, that is, the presence of two kinds of gland cells and the 

 absence of a reservoir for secretion granules common to all the 

 gland cells. It should be mentioned that Watanabe was the 

 first to direct especial attention to the luminous glands of ostra- 

 cods at Misaki. He read a paper on this subject before the 

 meeting of the Tokyo Zoological Society on January 23, 1897, an 

 abstract of which appeared in Japanese ('97). He states that 

 the maxillary glands secrete colorless transparent fluid and 

 yellow homogeneous substance. But he does not say whether 

 each gland cells produces these two substances or whether there 

 are two different glands for them. Miiller ('90, p. 248) clearly 

 states that he saw two groups of gland cells of different nature, 

 i.e., the secretion product of the upper group is found in the form 

 of droplets and does not take carmine stain at all, while that of 

 the lower group takes it. Furthermore he advanced the view 

 that light is produced by the interaction of these two substances. 

 He, however, seems to have failed to observe the correct topo- 

 graphical relation of these two kinds of cells. 



1 The general outline of the shell of Pypocypris japonica is more like that of 

 P. chierchiae (Miiller, '90, pi. 25, fig. 3) the posterior process being longer than 

 in the figure for this species. 



