I.I.AS On the Oriyin <>/ FtYx/uctid-i- Fnitnux. !" 



It will be seen that, us the analysis proceeds, each group furnishes a large 

 number of exclusively marine aud a very small number of exclusively freshwater 

 divisions; while the mixed fresh water and marine genera, omitting admittedly 

 exceptional cases, are very tVw indeed. Thus, to take the Spongiae as an example, 

 it is divided into six orders, of which only one, the Monaxonidae, is marked m.f.\ 

 all the rest are marine. Disregarding these, we find that the Monaxonidae break 

 up into live families, of which only one, the Renieridae, is marked /. m. This, 

 finally, is resolvable into several sub-families, all of which are marine, except one, 

 the Spoii-illina, which is exclusively freshwater. When this Paper was first penned 

 the Bpongillina were regarded as a compact family, clearly distinguished from 

 other Uenieriihi! by the possession of " statoblasts" ; but recent discoveries have 

 brought to light some ten species, belonging to four or five genera, which are said 

 to be without this characteristic feature; and it is quite possible that some of 

 these new forms may belong to genera otherwise known as marine. 



We now approach the inquiry as to how far the exemption we have predicted 

 of freshwater animals, from a free larval existence, is capable of verification. 

 Commencing with the sponges, we find, in this country, the closely allied genera 

 Euspongilla and Kpliydatia or Meyenia (Euspongilla Jluviatilis and Ephydatia lacus- 

 tris). Elsewhere the rest of the world has furnished hitherto some additional seven 

 or eight genera. Such of these (except Lubomirskia) as have been exhaustively 

 studied have been found to propagate by means of so-called "winter-eggs" or 

 statoblasts. These are modified internal buds or gemmules, which are provided 

 with a protective horny envelope, and generally one or more layers of surrounding 

 siliceous spicules. Within this protecting case the bud rests during the winter, 

 and on the a 1 vent of spring emerges as a young sponge. 



In tropical climates the statoblast is produced, not on the approach of 

 winter, but just before the dry season ; and it, no doubt, primarily serves, in this 



, as a means of protection against the fatal effects of dessication. Since, how- 



i, in the dry state, the envelope of these statoblasts contains a considerable 

 volume of air, which materially diminishes their specific gravity, it is possible, 

 as William Marshall has suggested, that their formation may serve a secondary 

 purpose ensuring for the sponge a wide dispersion by the agency of Un- 

 winds. 



The pressing need for a rigid attachment of the reproductive gemmules, 

 which exists in swift streams, or rivers liable to floods, is well illustrated by a case 

 mentioned by Marshall; for he finds that in Parmula brownii, from the Rio Negro, 

 the spieulur layer of the statoblasts is continuous with that of the hard, dense ske- 

 leton of the parent sponge, thus protecting them against all chance~ofj>eing washed 

 away till they can crawl out as young sponges and shift for themselves. On the 

 whole, so far as definitely ascertained facts go, they point unmistakably to the 

 general, if not universal, occurrence of a peculiar mode of propagation in the 



TEAMS. HOT. DUB. SOC., Jf.S. TOL. III. 



