516 SUMMARY OF CURRENT RESEARCHES RELATING TO 



or less aborted approximating their shape to that of the spined 

 fusiform acerates of Spongilla, gave rise to the suggestion that here, 

 possibly, had been, not merely a mechanical mixture by inter- or 

 super-position of species, but an organic hybridization produced by 

 the flowing together of the amoeboid particles of which the sponges 

 are composed, or even by a fertilization of the ova of one by the 

 spermatozoids of the other. 



It is important to note that the specimens were collected in 

 February, when the sarcode matter had nearly all been washed away 

 with, probably, accompanying changes in the presence or numbers of 

 the smaller spiculae. 



Boring Sponges.* — Mr. J. D. Hyatt, referring to papers in the 

 Journal of the Quekett Microscopical Club (in which the question 

 is discussed whether Cliona forms the burrows in which it is 

 found or whether they are excavated by annelids or other animals), 

 is convinced that there is one weak point characterizing all the ob- 

 servations, which invalidated to a great extent the conclusions on 

 both sides. This was, that dried specimens had been used, or, as one 

 author mentions, the live sponge occupying old shells and rocks. It 

 occurred to him that a study of the live sponge occupying the shells 

 of healthy, living molluscs, might present evidence for one side or the 

 other that had hitherto been overlooked, and he therefore procured 

 some oysters, a considerable number of which had shells tenanted by 

 Cliona. 



An exhaustive microscopical examination of these and similar 

 specimens, seems to him to establish, beyond a possibility of doubt, 

 that the sponge is, in this case at least, the only factor to be held 

 accountable for the burrows. The outer layer of the shells was 

 punctured with numerous holes, often many hundred, varying from 

 the ts to the rhs of an inch in diameter, generally occupied by the 

 osculse of the sponge. Between the outer and inner layers, and 

 extending laterally, the shell was almost entirely excavated, and the 

 space occupied by the sponge and its numerous spicules; while 

 extending inward from this sponge-mass were innumerable minute, 

 branching and ramifying burrows, uniformly and completely filled with 

 corresponding arms of sponge, many of which extend quite through 

 the interior layer of shell. The contact of these arms with the 

 external membrane of the oyster causes the latter to deposit at such 

 points an additional amount of lime carbonate, and the interior surface 

 of such shells presents the appearance of numerous little prominences 

 caused thereby. 



The only possible theory that will account for these burrows, if 

 they are not made by the sponge, is that they are the deserted ex- 

 cavations of worms ; but this theory is untenable, as it would be 

 necessary to suppose that the shell was once inhabited by an innumer- 

 able multitude of such worms ; otherwise the perforations through 

 the inner cell would have been closed, and all of these must have 

 retreated at the same time, so completely that no trace of them could 



* Amer. Mon. Micr. Journ., iii. (1882) pp. 81-4 (3 figs.). 



