SIBOGITA SIMULANS. 215 



from a union of the blind canals with the manubrium caused by further 

 centripetal growth ; this view is supported by the fact that all the adradial 

 canals are narrowest at the point of union with the stomach. There seems 

 no objection to this explanation ; for if the growth of the blind canals takes 

 place far enough they can do nothing except come into contact with the 

 manubrium ; and in the case of one of the canals of one of the younger 

 specimens the growth requisite to cause such a union would be less than 

 .5 mm. 



In the " Siboga " specimen of S. geometrica there were thirty-two canals ; 

 of which sixteen of the smallest join the other canals, radial and adradial, 

 at varying heights, instead of reaching the base of the manubrium. Their 

 condition is probably the result of the centripetal growth of blind canals ; 

 but whether this is the case cannot be determined except from study of 

 immature specimens. 



Tentacles. — In each of the two young specimens there are twelve ten- 

 tacles, one opposite each of the canals, radial or blind. In the older speci- 

 men there are thirty, one opposite each of the sixteen canals ; the others 

 arranged somewhat irregularly between the canals. In S. geometrica, not- 

 withstanding the larger number of canals, there were only sixteen tenta- 

 cles. In structure the tentacles, which are hollow, long, flexible, and 

 tipped with nematocyst clusters (PI. 41, fig. 9), agree closely with those of 

 S. geometrica. They have no basal bulbs (PI. 43, fig. 2), nor is there any pig- 

 ment in their bases. As in S. geometrica, they arise from the exumbrella 

 some little distance above the margin, — a feature seen also in Heterotiara. 

 Connected with the prolongation of the gelatinous substance of the exum- 

 brella beyond the level at which the tentacles arise is a slight lobing, alter- 

 nating with the tentacles (PI. 43, fig. 2), and as this was seen in life as well 

 as in the preserved specimens it is probably a normal feature. 



Gonads. — The four gonads are permanently interradial, and, as in 

 Heterotiara (p. 217), entirely discontinuous in the perradii. They are con- 

 fined to the walls of the manubrium, and each, as already described by 

 Maas (: 05 a ), consists of a double series of regular transverse folds (PI. 43, 

 fig. 1). In the Behring Sea specimen they are very large. 



Color. — In life the gonads were reddish brown, the bell faintly tinged 

 with blue. 



The capture of the two Eastern Tropical Pacific specimens on the surface 

 shows that this genus is not so purely intermediate as Maas c 05) supposed. 



