110 ■ THE MEDUSAE. 



tion requires observations on living specimens. They do in O. phosphorica, a 

 phenomenon I have myself observed at Bermuda. 



The presence or absence of basal bulbs on the secondary tentacles is 

 closely connected vpith the state of contraction of the latter. When the ten- 

 tacles are extended, their bases, which are free from nematocyst bands, are 

 pear-shaped, and of considerably larger calibre than the distal portions. In 

 a state of contraction, however, the filamentous, nematocyst-bearing portions 

 of the tentacles increase so much in thickness, corresponding to the decrease 

 in length, that the basal swelling may be entirely masked, and that region 

 may actually be of smaller calibre than the remainder of the tentacle. 

 Intermediate conditions are of course more numerous than either of these 

 extremes. Thus it is evident that the presence of basal bulbs is a less 

 important character than Browne's single specimen might suggest ; yet, 

 inasmuch as none of the numerous excellently preserved West Indian 

 specimens of O. pliospliorica which I have examined show any trace of basal 

 enlargements on even the most extended tentacles, it is not unreasonable 

 to retain this feature as one of the distinctive characters of O. ninr/ularis. 



The secondary tentacles terminate in nematocyst knobs (PI. 31, fig. 7). 

 The finer structure of the two types of tentacles has been fully described by 

 Goto (: 03). 



The number of otocysts is an important specific character in this form. 

 In the small specimens, 16-17 mm. in diameter, there is usually only one in 

 connection with each of the primary tentacles. In larger specimens, how- 

 ever, more of them are paired. In the largest specimens, 30-36 ram. in 

 diameter, single and paired otocysts are in the proportion of about four to 

 one (PL 31, fig. ^). When but a single otocyst is present at the base of 

 a primary tentacle it usually lies in the plane of the tentacle root (PI. 31, 

 figs. 3-5) ; and though there is some irregularity in this respect, I have 

 never seen a single otocyst lying at one side of the base of a tentacle. The 

 numerical condition of the otocysts is to be interpreted as phylogenetically 

 more primitive in 0. singiilaris than in 0. phosphorica; for while all authors 

 agree that in adults of the latter species the otocysts are invariably paired, 

 Mayer (: 04) has found that in the young they first appear singly, opposite 

 the bases of the primary tentacles. Each otocyst may contain either one or 

 two spherical otoliths (PI. 31, fig. 10). 



Gonads. — In the largest specimens the gonads, which first appear near 

 the ring canal, and with increasing development extend centripetally, occupy 



