768 CHARLES L. BOULENOER. 



four pen-adijil tentacles suspended from tlie umbrella edge. 

 These tentacles are slender and of great length when fully 

 extended ; at their bases they are swollen to form the very 

 conspicuous ocellar bulbs, each of which bears on its ex- 

 umbrellar surface a bright red eye-spot. The tentacles are 

 hollow, their cavities being continuous with that of the 

 circular canal ; the ectoderm is thickened at regular intervals 

 to form conspicuous transverse rings crowded with nemato- 

 cysts, and becoming very noticeable and almost bead-shaped 

 when the tentacles are fully extended. 



On examination of sections and maceration preparations of 

 these organs, one is again struck by the almost complete 

 absence of neniatoblasts or other interstitial cells, and we are 

 driven to the oidy possible conclusion, namely, that the 

 stinging-cells have developed elsewhere and have migrated to 

 the batteries on the tentacles. The large, eye-bearing bulbs 

 at the bases of the tentacles immediately suggest themselves 

 as possible nematocyst "factories," and sections of these 

 structures show that such a function must be assigned to them 

 (Text-fig. 1). 



An ocellar bulb consists of a mass of thickened ectoderm 

 crowded with small, irregulaily shaped cells and nematocysts 

 in various stages of development. The fully formed thread- 

 cells are devoid of cnidocils or other accessory structures, and 

 the capsules are never orientated so as to lie at right angles to 

 the sui'face ; we must, therefore, conclude that they do not 

 become functional in this region. In the centre of the bulb 

 the nematocysts lie in all directions, but near the base of the 

 tentacle we find a distinct tendency for these organs to be 

 arranged with their longer axes parallel with the structureless 

 lamella, a position, as mentioned above, characteristic of 

 mi"fratinQf thread-cells. 



Tiie above-mentioned facts lead us to the conclusion that 

 the stinging-cells of the tentacles, like those of the oral 

 battery, are not developed "in situ," but migrate into these 

 organs from " factories " situated in a more central position on 

 the medusa, in this case from the ocellar bulbs, whence a 



I 



