62 



CTENOPHORA. 



indicated. But even if these young stages really belong to M. ovum^), they cannot prove that the 



short tentacle-basis is characteristic of the grown Mertensia. On the contrary the tentacle-basis is 



unusually long, as I can show. 



In fig. II is represented the tentacle bases and the central part of the gastrovascular system 



of Mertensia, ovum, drawn from one of the specimens in the "Ingolf material. It shows the tentacle 



bases as rather long ^), characteristically curved 

 bodies, from the upper end of which the ten- 



inf '-t tacle proceeds; this shape the tentacle bases 



t 



have in all the specimens available, and it is 



' " likewise seen in the sketch made from a living 



, gg specimen by Vanh of fen (Nordisches Plankton, 



fig. i); also in Beroe compressa of Mertens, 



which*is, in my opinion, undoubtedly a syno- 



vnj iiym of M. ovuvi, they have the same shape 



and size. It may then possibly be right that 



the tentacle bases are short in the very young 



^^ r^Ti. specimens, as shown in the two figures of 



■ A. Agassiz — but in the larger specimens, 



from a size of ca. 3™", they are not "limited 



- / , , to the abactinal part of the spherosome", as 



l.m phv. ph. phv ivn maintained by Agassiz. His fig. 29 is too 



Fig. II. Pharynx and tentacle-bases of Mertensia ovum. d. diaphragm; 



inf. infundibulum; 1. m. longitudinal muscles; oe. oesophagus; little detailed for showing anything clearly of 



p. series of pigment spots; ph. pharynx; ph. f. pharyngeal (stomodaeal) ^|-jg shape and size of the tentacle-bases. 

 folds; ph. V. pharyngeal vessel; r. ni. radial muscles; t. tentacle; 



t. b. tentacle-basis. The peculiar feature of the pharyngeal 



vessels following close along the tentacle bases 



rests on a misunderstanding. The pharyngeal vessels join the pharynx as in other Ctenophores, 



as I have been able to see clearly both on sections and on the not sectioned material. What Agassiz 



has taken to be the pharyngeal ("lateral") vessel is evidently the tentacular vessel. 



Moser (Op. cit.) states that the tentacle bases, judging from the figures of Agassiz, are not 



longitudinally divided as in other Cydippids. This would appear to be really so, also on the preserved 



material; in sections it is seen, however, that the structure is in accordance with the usual type, only 



the two halves of the basis lie so close together, partly even overlapping one another, that it can 



only be seen in sections that there are really two parts as usual. It may be remarked that along 



each side of the tentacle basis is seen a rather conspicuous series of pigment spots (fig. ii); this 



would appear to be what Mertens mistook for the ovaries. 



1) It is peculiar that Fewkes does not mention Agassiz' description of the young Mertensia in his short note on 

 Mertensia ovu?n (On certain Medusa from New England. Studies from the Newport Marine Zoological Laboratory. Bull. Mus. 

 Comp. Zool. Vol. XIII. 1887. p. 212), where he records that he has traced the development of .some Ctenophoran eggs "into young 

 Mertensiffi, (which) are possibly of this species". 



2) The oral end of the pharynx being destroyed in the specimens preserved it cannot be seen there how far down 

 towards the mouth the tentacle basis reaches; from Vanhiiffen's sketch (fig. i) of a living specimen they are seen to reach 

 nearly to the mouth. Is is worth mentioning that in a specimen, which can scarcely have been more than 3"'™ long, the 

 tentacle bases have already the same shape and relative length as in the grown specimens. 



