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2. o cm. The marginal tentacles were from 2.5 to 3.0 cm. in length, their diameter at the 

 base being about 1 mm., while the labials had a length of only 2.0 mm. 



Colouration. — The column was of a pale violet brown colour, as were also the 

 disc and the labial tentacles. The marginal tentacles were colourless. 



Structure. — On laying open the column by a dorsal longitudinal incision, the oral 

 disc is seen to be deeply concave and longitudinally ridged. The stomatodaeum possesses a 

 well developed siphonoglyph, on either side of which it becomes markedly 

 longer and then diminishes rapidly as it is traced dorsally, the lower border 

 thus showing a rounded projection on either side of the siphonoglyph. 



The protocnemes of the first couple are very short, hardly projecting 

 below the lower border of the siphonoglyph (Text-fig. X). The second and 

 third couples are sterile, the second being about two-thirds the length of the 

 column and the third distinctly shorter. The fourth couple constitute the 

 telocnemes; they are fertile and extend to the aboral pole. The deuterocnemes 

 have a well marked quartette arrangement, the formula for each quartette 

 being S, f, s, F. The larger macrocnemes of the two or three ventral quar- 

 tettes extend almost to the aboral pole, but those of the remaining quartettes 

 diminish rapidlv toward the dorsal surface. The shorter macrocnemes of each 



r J Fig. X. 



quartette are much shorter than the longer ones, those of the ventral quar- Diagram showing the 



.. . , . , r , arrangement of the 



tettes hardly extending to half way between the lower border ot the stoma- mesenteries of Packycer . 

 todaeum and the aboral pole; the longer microcnemes are slightly shorter ianthus morwstichus. 

 than the shorter macrocnemes and the shorter microcnemes extend but a short distance beyond 

 the lower border of the stomatodaeum. Craspedonemes occur on the macrocnemes below the 

 stomatodaeum, but were not found along the margin of the gonophoric portions of the 

 mesenteries as in P. fimbriatus. 



Larval Forms. 



Genus Arachnactis M. Sars. 

 Synonym : Arachnactis M. Sars, 1846. 



Arachnactidae whose larval forms have a spherical body in the early stages, later be- 

 coming elongated. Marginal tentacles long and slender, in the earlier stages several times the 

 length of the column ; the median unpaired marginal tentacle appears only after the development 

 of these corresponding to the fourth intermesenterial chamber. 



The genus Arachnactis was established in 1846 by M. Sars for the reception of 

 A. alöida, a free-swimminer form found in the autumn and winter at Floroe Island, off the 

 coast of Norway. Since its discovery this species has frequently been under observation, notably 

 by Boveri (1890) Vanhöffen (1895), Fowler (1897) and E. van Beneden (1898). The last 

 named author showed that acontia occurred upon the fourth couple of protocnemes, and his 

 fiorures of forms with nine and thirteen marginal tentacles show that the second and third 

 couples possess a wavy filament, their sterile or microcnemic character being thereby indicated, 



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