40 THE MEDUSAE. 



Haeckel ('81, pi. 29) and by Vanhoffen (: 02% taf. 5, fig. 32) for this species 

 (fig. 1). In the small specimens there is considerable variation in the 

 breadth of the furrows. In a specimen with the disc 20 mm. in diameter 

 the condition, as represented on PL 10, fig. 9, is that described by Van- 

 hoffen (: 02*) as typical of A. verrillii Fewkes, the furrows being very narrow. 



I should have thought that this specimen 

 belonged to that species had it not been 

 that other small specimens showed more or 

 less intermediate conditions. One, 15 mm. 

 in disc diameter, is especially instructive, 

 since in it about half of the furrows are 

 broad, the remainder narrow, while in the 

 two smallest specimens with discs respec- 

 tively 7 and 8 mm. in diameter, most of 

 the furrows are broad, but in both a few 

 are narrow. Apparently, then, not all the 

 '*^" ■ radial furrows in this species attain their 



typical "broad" condition until a considerable size is attained. It is inter- 

 esting to note that both specimens of this species recorded by Vanhoffen 

 (: 02% p. 13) were large, the central discs measuring respectively 37.5 and 

 47 mm. in diameter. 



At first such variability in the form of the radial furrows would suggest 

 that they were of little systematic importance. Such, however, does not 

 seem to be the case, for Vanhoffen ( : 02") has found that in a large series 

 (nineteen specimens) of A. verrillii they are constantly narrow, both in large 

 and in small individuals. This discovery suggests the very interesting con- 

 clusion — one, however, which may have to be modified later — that A. 

 verrillii retains permanently a character which occurs, it may be only irreg- 

 ularly, in the young of the closely related A. ivi/villei; but whether the two 

 are really valid species can hardly be settled without studies on still more 

 extensive series from all oceans. 



The present specimens support Vanhoffen's (: 02"^) contention that there 

 is normally one less furrow than tentacle (PI. 10, fig. 9), and that the full 

 number of antimeres is attained at an early stage. 



Maas's recent (: 03, : 04'') discovery of areas of adhesion subdividing the 

 tentacular canals at their bases in A. valdiviae and A. haird'd gives fresh interest 

 to a study of the canals. 



