AN ENTOPROCTAN POLYZOON (BARENTSIA BENEDENl). 839 



ventral muscle which occurs in the simple, unjointed Entoproctan, Myosoma spinosum, 

 Robertson. 



The central nerve ganglion is frequently apparent. It lies, as viewed laterally in 

 well-developed specimens, between the ovaries, in line almost with their anterior 

 margin ; the posterior portion being concealed by the ovaries, the anterior free. Seen 

 in this direction, it is oval in shape, tending sometimes to have the upper or lower 

 surface flattened. Measurements show a variation in size of from 6m height by 

 10m length to 13m by 18m, but a common size is 9m by 12m. Seen in an antero- 

 posterior direction, the ganglion is almost trapezoid, the sides tending to be a little 

 concave. In this respect it differs considerably from the elongate, distinctly bilobed 

 ganglion found by Harmer in Loxosoma # and by Foettinger in Pedicellina benedenij 

 and resembles the structure figured by Foettinger (op. cit., pi. x. fig. 25) from 

 Pedicellina belgica. 



Note on Living Specimens. 



After sending the first small colony, which was found dead on arrival from Hull, 

 Mr Thompson succeeded in having living specimens transferred to Edinburgh in 

 February 1909. These were kept under observation for a week. The colonies were 

 ever active ; a single stalk bent over with a sudden movement, and in so doing struck 

 a neighbour ; this caught up and spread the alarm, until the whole colony appeared to 

 be a crowd of angry individuals, nodding and colliding, and bending suddenly into loops 

 and circles as if they squirmed in pain, then gradually straightening again. The lopho- 

 phore and tentacles showed much diversity in expansion. Often all lay widespread and 

 taut in a single plane, while in another common resting position the lophophore was 

 expanded, while the tentacles, not at full length, rose perpendicularly above the margin, 

 their tips curving at the same time a little inwards. Generally the tentacles were 

 altogether retracted during the wild bendings of the stalk, but occasionally movement 

 would take place, the tentacles remaining expanded the while. A touch with a dissect- 

 ing needle did not in most cases produce immediate reaction on the part of an individual. 

 That regeneration is frequent is evident by the number of young heads on old shoulders, 

 and of headless but living and active stalks. 



For the dimensions of the Hull specimens see table on p. 845. 



Before concluding the descriptive portion of this paper, I must refer to two examples 

 of regeneration which occurred, not in the Hull specimens, but in examples of Barentsia 

 gracilis. In a specimen from Port Erin (PI. I. fig. 7), a new calyx was found 

 already well developed ere the old head had dropped off— a condition illustrating a 

 normal mode of rein vigora ting the animal, similar to the periodical shedding of the 

 polyps which has been described in genera of Gymnoblastic Hydroids. 



* Harmer, S. F., op. cit., p. 270, pi. xix. fig. 1. 



t Foettinger, A., " Sur l'anatomie des Pedicellines de la cote d'Ostende," Arch. Biol., vol. vii., 1886, p. 321, 

 pi. x. fig. 18. 



