242 SUMMARY OF CURRENT RESEARCHES RELATING TO 



per cent. (4 per cent, of all the organic remains) are whole or frag- 

 mentary amphidisks of Spongillidce ; the absence of entire gemmules 

 is explained by the distance which Ehrenberg's dust had travelled, 

 viz, to Europe from (probably) North-west Africa. 



By experimenting directly on gemmules of Spongilla lacustris 

 and nitens, by drying them for 8 days, piling 50 of each species 

 together into one heap on a smooth plate, and blowing at them with 

 a bellows, it was found as the result of this operation, repeated six 

 times, that the gemmules of ;S^. nitens were scattered to a greater 

 distance than those of lacustris, viz. 75 per cent, beyond a radius of 

 5 centimetres, as against the 64 per cent, of those of the other 

 species which stayed within this radius. 



The gemmule of the South American species Parmula Brownii has 

 a very compact spicular shell, the spicules show a tendency to radiate 

 from points at which the capsule is in contact with the true envelope 

 of the gemmule : the latter envelope is covered with conical eminences 

 which fit loosely against the outer capsule while dry, but come closely 

 against it after soaking for some time in warm water — probably 

 showing that it is a special arrangement to allow of the expansion 

 of the germ, the outer capsule having no opening. The shield-like 

 spicules overlap and cover all the surface of the inner envelope 

 except the eminences just described. The outer capsule is usually 

 firmly united to the surrounding skeleton. The sponge is known to 

 affect, as its rooting places, stones which are alternately wetted and 

 left dry. Thus, the close connection of the skeleton with the capsule 

 secures it from being detached when dried, and the overlapping 

 arrangement of the shield-like spicules prevents excessive collapse 

 of the tender underlying envelope. 



The heaviness of the gemmules of Spongilla lacustris, and their 

 projecting spicules (like the hooks of Polyzoan statoblasts) tend to 

 anchor them and prevent undue rapidity of transportation by currents. 

 The gemmules of the allies of S. fiuviatilis are heavier than those 

 of lacustris and allies, and hence are less mobile and better adapted 

 to rapid streams. The three layers of amphidisks in the gemmule 

 of Meyenia mirahilis Eetzer (a recently described species) are perhaps 

 an adaptation to very rapid waters. 



Marshall thinks it not inconceivable that external circumstances 

 (e. g. long sojourn in still water) might transmute Spongillce (Eu- 

 spongilla) into Meyenice, and vice versa ; of the present occurrence of 

 these changes perhaps Euspongilla Jordanensis var. druliceformis 

 Vejdovsky affords an example in the transitional characters of its 

 gemmule spicules. 



European Fresh-water Sponges.* — Dr. P. Vejdovsky supplements 

 his former study of this subject f by some additional observations : 

 firstly he establishes the new species Ephydatia amphizona for the 

 form previously described by him as Eph. Mulleri forma B., reserving 



* Abh. Bohm. Gesell. Wiss., 1883. See Ann. and Mag. Nat. Ilist,, xiii. (1884) 

 pp. 96-8 (1 pi.). 



t See this Journal, iii. (1883) p. 858. 



