196 THE MEDUSAE. 



by the Amboina specimens recently described by Maas (: 0G C ). The collec- 

 tion from the ''Siboga" (Maas, : 05) belongs to a still further advanced stage. 

 The bell is higher than broad, the gelatinous substance thick, especially at 

 the apex. Maas (: 05, p. 11) states that in large individuals the outline is 

 somewhat prismatic; but the great majority of the present specimens are 

 circular in cross section, although a few are more or less distorted by 

 preservation. 



The largest number of tentacles per bundle in our series is thirteen (PI. 44, 

 fig. 7), in a specimen 7 mm. high. Maas (: 05) has noted twenty in still larger 

 specimens. In specimens 1-2 mm. in diameter there are only three or 

 four per bundle ; but the number increases steadily with growth. It appears 

 that shortness of the tentacles is distinctive of this species, as Maas has 

 suggested, for even in life I have never seen them reach a length greater 

 than one half the height of the bell. Such excessive reduction of these 

 organs as he has figured (:05, taf. 1, fig. 8) for the " Siboga " specimens is 

 probably due in part to contraction and preservation. The ocelli lie on the 

 inner (oral) faces of the tentacular bases ; but I have seen no actual evidence 

 that this location is associated with a habit of carrying the tentacles curved 

 upward as he has suggested, and as Agassiz and Mayer have figured them 

 (: 02, pi. 2, fig. 8). On the contrary, in life the tentacles were very flexible, 

 being alternately expanded and contracted, and often streaming behind the 

 bell, as in the common B. sitperciliaris from the Atlantic. 



The form of the manubrium is variable. Maas has already noted that 

 " Man konnte das lebende Tier . . . fur eine Margelis, das conservierte fur 

 eine Hippocrene halten" (: 05, p. 11), the manubrium in life being long, 

 after preservation very short. This species, when small, passes through 

 what may be called a Margelis stage. In the smallest specimens the manu- 

 brium is barrel-shaped, its base being narrow. In larger specimens it is 

 broader basally, though showing much variation with different degrees of 

 contraction. In the largest specimens its base becomes very broad, an 

 outline associated with the appearance of the gonads; as Maas has 

 shown, even when it is broadest the radial canals do not originate at its 

 corners, but can always be traced to its centre where they meet in a cross. 

 In outline, as viewed aborally, the manubrium of larger specimens varies 

 from nearly circular to cruciform, a variation correlated with contraction 

 and perhaps with the state ul' nutrition of the organ. The mouth is usually 

 cruciform (PI. 44, fig. 6). 



