CTENOPHORA. 



71 



auch noch werden, dass sich das Tier so kontrahieren kann, dass aus der kugeligen Form eine zylin- 

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

 z. B. die Tentakelbasen sich dem Magen nahern" (p. 144). My observations are in 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 nearly 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 nn- 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 



o.rsh. 



► - tsh 



phj 



ph 



not given. 



,--th. 



Chun (Monogr. p. 242) states, as an instance showing ^.^^^ pi.urobrachia piu,^, 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 Ktistenpunkten, je nach der Haufigkeit von ^ ^ ^.jj opening of the tentacle sheath. 



heftigen Winden, ausgiebigen Schwankungen unterworfen 



sind" that "im AUgemeinen die amerikanische Pleurobrachia rhododactyla doppelt so gross (ist), als 



die offenbar mit ihr identische Cydippe (Pleurobrachia) pileus der stiirmischen Nordsee". This is 



doubtless not correct. The Plnirohr. pilnis abounds in the North Sea in sizes by no means smaller than 



