MNEMIOPSIS LEIDYI. 



21 



handle can plainly be seen, on dark nights, by the light produced 

 by this illumination. The seat of the phosphorescence is confined to 

 the rows of locomotive flapjjers, and so exceedingly sensitive are they 

 that the slightest shock to the jar in which these Mednsse are kept 

 is sufficient to make them plainly visible by the light emitted from 

 the eight phosphorescent ambulacra. This species is long, almost ellip- 

 soidal, when at rest. (Fig. 22.) The auricles extend about one third 

 then' length beyond the oral aperture (o. Fig. 22), taking their origin 

 on a level with the eye-speck (a, Fig. 22). The prolongation of the 

 chymiferous tubes, and their manner of anastomosing, is exceedingly 

 simple ; we find nothing of the complicated bends and turns (Fig. 23) 



of the same tubes which we have in Bolina alata (Fig. 16). Bolina 

 alata ranks among the most perishable of aU our Medusae ; but this 

 species seems to be very hardy, as I kept one large specimen alive 

 for three weeks, dm-ing the whole of my stay at Naushon. This speci- 

 men also laid eggs, which were developed into small MnemiopsidiB, 

 after passing through stages in which it was almost impossible to say 

 whether the Medusa was a young Pleurobrachia or not. As is the 

 case in Bolina, the long tentacles, the globular outline of the young, 

 resembled so closely the young of Pleurobrachia, which were develop- 

 ing at the same time in another bottle, that freqviently I would be 

 unable, after leaving them for some time, to decide at once to which 



Fig. 22. Mnemiopsis Leidyi seen from the broad side, o, starting-point of branch of tentacu- 

 lar apparatus extending along the furrow, /, to a, the base of the auricles. 

 Fig. 23. The same as Fig. 22, seen from the narrow side. 



