Species q/" Uruguay a, Carter. 11 



a fresh development of gemmules at the base of each, indi- 

 cating that there has been a break in the life of the sponge 

 and that the fresh growth, though immediately overlying that 

 of the previous season, is quite distinct from it *. The re- 

 striction of the gemmules in U. Macandrewl to the base of the 

 sponge, therefore, confirms the idea of its perennial growth. 



It also seems probable that gemmules are not produced 

 after the first year of the life of the sponge, and that when 

 the conditions are sufficiently favourable to allow of its con- 

 tinued growth for longer periods there is no repetition of this 

 mode of reproduction. It might also well happen that under 

 these circumstances gemmules would cease to be produced, 

 and this may be the case in U. corallioides. 



The presence of gemmules in some forms of Uruguaya 

 and the minute structural resemblance between their amphi- 

 disc-spicules and those of certain species of Meyenia indicate 

 that these sponges are genetically related to some common 

 gemmuliferous ancestor, and thus tend to negative the sup- 

 position of Di\ W. Marshall that the sponges of the former 

 genus may have been derived independently from marine 

 forms which have become adapted to fresh water. The sug- 

 gestion of Dr. Marshall that freshwater sponges may be of 

 polyphyletic origin seems very probable, more especially as 

 regards those occurring in Lake Baikal ; but the facts brought 

 forward in the present paper point to the desirability of re- 

 newed careful search before speculating with confidence on 

 the absence of gemmules either in Lubomirskia or in he 

 Congo forms of Uruguaya. 



In conclusion, I wish to express my thanks for the kind 

 assistance in the preparation of this paper which I have re- 

 ceived from my friend Mr H. J. Carter, F.R.S., from Mr. T. 

 Higgin, F.L.S., of Liverpool, Dr. C. Stewart, F.L.S., of the 

 Eoyal College of {Surgeons, Mr. E. Howarth, of the Sheffield 

 Public Museum, and from the authorities of the British 

 Museum of Natural History. 



EXPLANATION OF PLATE IV. 



Uruguaya repens, n. sp. 



Fi(/. 1. A fragmunt of the skeletal mstili, sho-wing the arraugemeut of the 



spicules. Enlarged 00 diameters. 

 Fig. ^2. Detached spicules of the skeletou. Enlarged 100 diameters. 



* This is well shown in a specimen of Meyenia Leiclyi, Bowbk., sp., 

 which has been kindly sent to me by Mr. Edward Potts, of Philadelphia. 

 In this there are several skeletal layers overlying each other, and there is 

 a platform of gemmules at the base of each . 



