CTENOPHORA. 



71 



audi noch werden, dass sich das Tier so kontrahiereu kanii, dass aus der kugeligen Form eine z>lin- 

 drische wird, wobei die inneren Organe sich in die Lange strecken und teihveise zuzammenriicken, 

 z. B. die Tentakelbasen sicli dem Mageii naherii" (p. 144). My observations are iu full accordance 

 herewith. In fig. 13 a — b are figured a pair of specimens showing such great differences in the arrange- 

 ment of the radial canals of the gastrovascular system, that one would scarcely think it possible that 

 they could belong to the same species. Especially the direction of the main transverse canals is differ- 

 ent, in one (a) horizontal, in the other (b) nearly vertical; similarly the position of the tentacle base is at 

 the level of the upper end of the pharynx in one, nearly at the middle of the pharynx in the other 

 specimen. Also the shape is very different, the one nearh- spherical, the other subcylindrical. But all 

 transitions between these two extremes occur among the specimens from one and the same locality, 

 so that there cannot be any doubt that these differences are due either to individual variations or to 

 the different stages of contraction on preservation (or to both). I have not had occasion to examine any 

 large number of specimens of this species in a living state, so I cannot say definitely whether such 

 differences really occur in the living specimens; but for my own part I do not doubt that these dif- 

 ferences are mainly due to the contraction on preservation. Likewise I suppose that the more cylin- 

 drical shape, which Dr. Moser suggests to represent a growth change, is due to the preservation. — 

 Observations on living specimens are necessary to decide these questions. 



A peculiar variation was found in a few specimens, 

 viz. the infundibular canal being split up in a greater part 

 of its length (Fig. 14); in one case it was even divided in 

 the whole length. 



Regarding the colour of the tentacles it should be 

 mentioned that there are two laterally placed, close series 

 of pigment spots; these series continue upwards, along 

 the sides of the upper part of the tentacle basis, receding 

 somewhat on passing over from the tentacle to the basis. 

 This arrangement I have found in all the specimens exam- 

 ined, so that it very probably is a constant feature of this 

 species. In PI. 3, fig. 5 of L. Agassiz' memoir, quoted above, 

 these series of pigment spots are indicated, their receding at 

 the basis of the tentacle being well .shown, while otherwise 

 the arrangement in two distinct series along the tentacle is 

 not given. 



Chun (Monogr. p. 242) states, as an instance .showing ^.^^^ pi,,.,.obrachia pile,.., seen from the tenta- 



"wie die relativen Grossenverhaltnisse derselben Art an den cular plane; showing forking of infundibular 



canal. Letters as in Fig. 13. besides: ot otolith; 

 verschiedenen Kiistenpunkten, je nach der Haufigkeit von ^ ^ ^.jj opening of the tentacle sheath. 



heftigen Winden, ausgiebigen Schwankungeii uuterworfen 



sind" that "ini Allgemeinen die amerikanische Pleurobrachia rhododactyla doppelt so gross (ist), als 



die offenbar mit ilir ideutische Cydippe (Pleurobrachia) pileus der stiirmischen Nordsee". This is 



doubtless not correct. The Pleurobr. pileris abounds in the North Sea iu sizes b\- no means smaller than 



ph_t 

 ph - 



-th. 



