the Freshwater Sponges. 407 



all times of the year. The branched sponges living at the 

 bottom of tlic river Spree have hitherto only contained smooth 

 gennnnlcs. In the broad sponge which grows upon boards and 

 posts, both forms were met with, but not in the same piece. 

 The ordinary contents of the gennnules have already been ac- 

 curately described by Meyen (Miiller's Archiv, 1839, p. 83), 

 where it is shown that the amphidisks are constituents of the 

 gcmmules. In several specimens, the globular arrangement was 

 not present; the finer granules exhibiting molecular motion 

 being present in great numbers. 



In regard to the destiny of the gemmules, Meyen supposed 

 that a polyp-like animal was developed in them, and escaped 

 from the pore. Grant had previously stated, that in the marine 

 sponges, at certain times of the year, infusorial beings, ciliated 

 at the anterior end of the body, are produced ; these subse- 

 quently becoming fixed, and forming sponges. 



In the freshwater sponges. Grant did not find the gemmules 

 exhibiting motion, nor were cilia present. Dujardin mentions 

 two forms of reproductive bodies in the freshwater sponges, — 

 the gemmules and the ciliated bodies found by Laurent. John- 

 ston states, that at certain times of the year the gemmules 

 separate from the general mass of the sponges ; that they are 

 then furnished with locomotive organs, like Infusoria, with which 

 they might easily be confounded. The results of the observa- 

 tions of Hogg and Carter have already been published in the 

 * Annals.^ Carter found no trace of swarm-spores. The course 

 of development described by him by no means, however, ex- 

 cludes the possibility of his having overlooked them. But the 

 observation that insular groups of germs occur, the contents of 

 which are gradually converted into the variously shaped cells, is 

 correct. 



During the month of June of the present and last year, I 

 have frequently observed ciliated swarm-spores of the freshwater 

 sponges ; and a number of circumstances prove that they are 

 integral components of the sponges. 



That the entire gemmule is converted into the swarm-spore, 

 as supposed by some obsenxrs, is incompatible with the facts to 

 be presently described. The shell of the gemmule and the 

 cortical substance of the swarm-spores are totally diflferent in 

 their properties. Very frequently empty shells of the gemmules 

 are met with ; and nothing is opposed to iNIeyen's supposition, 

 that their inhabitants escape from the pore. 



The Swarm-spores. — I first detected these after leaving I'ccent 

 sponges for some hours in a glass full of river- water. They are 

 visible even to the naked eye, being about j'j inch in length, 

 and about j^^ in their broadest diameter. They are oval, and 



