MNEMIOPSIS LEIDYI. 



21 



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

 by this illimiination. The seat of the jihosphorescence is confined to 

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

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

 is sufficient to make them plainly visilde 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 

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

 on a level with the eye-speck («, 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) 



Fi-. 22. 



Fig. -23. 



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

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

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

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

 men also laid eggs, which were developed into small Mnemiopsida^, 

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

 Avhether 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 frequently I would be 

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



Fig. 22. Mneniiopsis Lciilyi scon from tlip broad ."ide. o, startin<:-i)oiiit of branch of tentacu- 

 lar apparatus extendiui; along the fnrrow, /', to a, tin' ba.so of the auricUs. 

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



