76 THE MEDUSAE. 



related to each other that, although the evidence at present indicates 

 that they are distinct, we must recognize the possibility that further 

 research may prove that they are really only two varieties of a single species. 

 Among the differences between them which Maas (: OG**, : 06°) enumerates, are 

 size, color, stage of development at which the gonads appear, and number 

 of otocysts. It seems to me that the last of these is of much the greatest 

 systematic importance. No doubt S. bitetitaculata is larger than S. mediterranea, 

 and as a rule more highly colored, but both size and color are well known 

 to be variable characters among Hydromedusae, and to be dependent largely 

 on the food supply of the specimens in question. The question of the time 

 of appearance of the gonads is likewise an unsafe criterion, because it is 

 very variable, for it has been conclusively shown by Browne (: 05'') that 

 even very small specimens of S. bitentaculata (size unfortunately not given) 

 possess gonads on the gastric pouches, although it is only large specimens 

 (9 ram. in diameter) which have them developed on the central portion of 

 the stomach ; and Maas himself has stated that, while some specimens 8 mm. 

 in diameter have no gonads at all (:05, p. 75), others of the same size are 

 sexually mature (: 06", p. 99). 



The question of the number of otocysts seems to me much more impor- 

 tant. In the case of S. mediterranea we have the positive statement of the 

 brothers Hertwig (78) that there are never more than eight otocysts, two 

 to each quadrant. In S. bitentaculata, however, Maas (: 05) has found as many 

 as thirty-two of these organs in large specimens. Furthermore, not only is 

 the number in S. mediterranea strictly determinate, but the total number is very 

 early attained, while there is reason to believe that in S. bitentaculata, on the 

 contrary, the number increases constantly with growth, as noted by both 

 Browne (: 05'') and Maas (: 05, : 06"). It is important also to note that the 

 number of sense organs does not increase with equal rapidity in all quadrants 

 of the margin, a phenomenon I am able to trace in the present specimens. 



The identity, with one or the other of these two species, of the various 

 specimens described by Haeckel ('79) and Mayer (: OO*") under the name 

 S.dissonema is not easy to settle ; but inasmuch as all these specimens agree 

 in having only eight otocysts whatever their size, and since all are of com- 

 paratively small size, the largest, from the Canaries, being only 8 mm. in di- 

 ameter (Haeckel, '79), and may become sexually mature when only 3 mm. in 

 diameter (Mayer, : 00''), it is probable that they really belong to S. mediterranea, 

 not to S. bitentacidata. The same is true also of Aeginella mulleri Haeckel, which 



