Freshwater Polijzoon from S. Africa. 269 



submersion of a great many of tlie statoblasts ; the sunk 

 statoblasts having been rendered capable of germination by 

 deprivation of oxygen rise again, buoyed up by the annulus, 

 after the entangling weed has completely decayed, and 

 germinate at the surface. It would be interesting to know 

 whether there are any direct observations on this point and 

 whether all the statoblasts of Cristatella are equally buoyant. 

 We cannot, of course, argue from one case to another ; the 

 conditions in a S. -African vlei are very different from those 

 wliich obtain in the waters in which Cristatella lives. But 

 it is wortli while to note the various functions which have 

 been attributed to the hooks. 



Oka's remarks on the annulus and hooks are specially 

 interesting in connexion with the present species. He lays 

 stress on the importance as distributing-organs of the iiooks 

 on the statoblasts of Cristatella and of Pectinatdla magnifica, 

 " in which the annulus is but weakly developed and cannot 

 serve as more than a mere buoy,'^ contrasting this condition 

 with the extreme insignificance of the minute hooks of 

 Pectinatella gelatinosa, in which the annulus is very large 

 and shows curvature. 



In Lophopus capensis, in which the annulus does not even 

 serve as a buoy, hooks would evidently have great importance 

 in more than one respect, and to this is no doubt due their 

 marked development. 



These foregoing cases might suggest that in general an 

 inverse relation would be found to exist between the degree 

 of development of the annulus and of hooks ; but this does 

 not prove to be supported by the facts. The relative dimen- 

 sions of the central capsule and the annulus in Plumatella 

 vesicularis, for example, which has no hooks, are, judging 

 from Braem's figure, much the same as in Lophopus capensis, 

 the total amount of air-space being, if anything, smaller in 

 P. vesicularis. But the thickness of the wall of the central 

 capsule of Lophopus capensis is noticeably greater than in 

 any other statoblast I have seen figured ; and as chitin is 

 considerably heavier than water (sp. gr. 1"4), tliis may, 

 perhaps, be sufficient to account for the incapacity of the 

 statoblasts to float. 



Apparently a period of cessation of respiration is not 

 necessary to render the statoblasts of Lophopus capensis 

 capable of germination, for those which I have been dealing 

 with had but newly escaped from the parent colony when 

 they came into my possession, and shortly afterwards the 

 greater number of tliem hatched. 



On Nov. 5, 1907, 1 first noticed that one or two of the 



