No. 5-] VARIATION A. \IOi\G HYDROMEDUSAE. 



2 4 I 



suggest that there had been complete unions of these partial 

 canals at an earlier stage and that the present condition was 

 the result of atrophy such as is shown in Figs. 6 and 9. It 

 would seem therefore quite just to conclude that these several 

 structures, spurs, partial canals, loops, etc., have had their 

 development usually from the central pouches or canals and 

 not from the peripheral or marginal canal. 



The unusual specimen, to which reference is made in this 

 connection, is shown in Fig. 13 of the text. It would appear 

 to partake somewhat of the nature 

 of a monstrosity and in some re- 

 spects of the nature of a marginal 

 bud, suggestive of a secondary 

 medusa. Aside from the general 

 form there is little to confirm this 

 possibility ; there is no sign of 

 manubrium ; and the canals and 

 tentacles are quite continuous with 

 those of the primary medusa. As 

 will be noted, there are vestiges of 

 gonads upon the peripheral termination of the median canal, 

 while the branches are wholly devoid of any signs of such 

 structures. Only a single specimen of this character was 

 found and it exhibits another aspect of erratic variation. 



TIG. 13. 



Gonads. 



In the comparisons of gonads only specimens apparently 

 sexually mature were taken (as noted before, no distinction 

 was made between sexes). In the cases wholly devoid of 

 gonads the size and other organic conditions were considered 

 as sufficient to warrant the conclusion that they were probably 

 of such age and general development as are usually correlated 

 with perfect sexual maturity. In the whole number of speci- 

 mens examined 3.6 per cent showed numerical variation of the 

 gonads ; of specimens with less than the normal number, two 

 per cent; of those with more than the normal, 1.2 per cent; 

 of specimens without trace of gonads, .4 per cent. As will be 



