TUNICATE RHIZOMOLGULA GLOBULARIS. 157 



localities (Baffin Bay and Hei'schel Id.), all within the Arctic 

 Circle ; and from a place in Alaska outside that circle. The 

 material from Spitsbergen fills in a gap in the circumpolar 

 distribution. 



Depth. Shallow water to 40 metres. 



There are present in all the examples examined numerous 

 specimens of a species of parasitic protozoa of the group Sttctoria 

 with a globular sessile body 0'5 to 0-1 mm. in diameter and with 

 one or more tufts of granular slender, vase-shaped tentacles 

 (PL I. figs. 2-4, 9, 10). 



When the Ascidian is cut in half transversely and the front 

 half turned back, the Suctoria appear — under a lens — like snow- 

 balls scattered over the tentacles (fig. 2). They are distributed 

 over the antei'ior aspect of the tentacles and front wall of the 

 peripharyngeal groove, and never on the posterior wall oi' the 

 area behind it ; they are especially abundant near the upper end 

 of the endostyle and dorsal lamina. This curiovis distribution 

 led the writer into mistaking the Suctoria for sensory organs of 

 the Ascidian, and he has to thank Dr. W. T. Caiman for suggesting 

 that the " knobs '" were probably parasitic Protozoa. 



In 1894 Dr. R. Gottschaldt (Jenaische Zeitsch. Bd. xxviii. 

 p. 343) described and figured Suctoria found behind the tentacles 

 of the Ascidians Polyclinopsis haeckeli Gottsch. and Synoicum 

 titrgens Phipps from Spitsbergen. The Suctorian figured by 

 Gottschaldt difiers from the present one in having knobbed 

 tentacles. Dr. Gottschaldt regards his species as symbiotic 

 rather than parasitic, because the remains at least of the sucked- 

 out Protozoa bi'ought to the Ascidian fall to the lot of the latter; 

 whereas some of the ciliated Infusoria might, in the absence of 

 the Suctoria, have escaped altogether. 



EXPLANATION OF PLATE I. 



Figures of Mliizomolgula glohularis (Pallas). 



Pig. 1. A rather large specimen. Nat. size. 



Fig. 2. Anterior part reversed, of a specimen cut across transversely, showing the 



posterior aspect of the tentacles. Ti, primary tentacle-s ; Tu, secondary ; 



Jf, mouth ; At, atrial opening ; P, perijjharyngeal bands and groove : 



c?^, dorsal tubercle ; dl, dorsal lamina; J5w, endostyle; /", folds of branchial 



sac; bs, cut edge of branchial sac. X 10. 

 Fig. 3. Groups of Sttctoria on or near the anterior peripharyngeal band, near the 



end of the endostyle. JE«, endostyle; P', posterior pharyngeal band; 



P", anterior ditto ; T;i/l, the "knoh-like Suctoria. X 18. 

 Fig. 4. Group of Suctoria in epibranchial area near dorsal tubercle, clt. X 18. 

 Fig. 5. Part of tentacular ring and tentacles of four orders (mainly diagrammatic). 



>< 30. 

 Fig. 6. Primary tentacle, antero-lateral aspect. X 60. 

 Fig. 7. Primary tentacle, posterior aspect. Partly diagrammatic. X 40. 

 Fig. 8. Primary tentacle, anterior aspect. Partly diagrammatic. X 40. 

 Fig. 9. A Suctorian, with a nearly central nucleus-like body, and one tuft of 



sensory hairs. X 280. 

 Fig. 10. Part of a Suctorian. X 1400. 



