72 Dr. G. J. Ilinde on the Genus Hiuclia. 



in reality, as already mentioned, chalcedony and quartz. 

 This I have proved by testing with acid and by polarized light 

 some of the same specimens from New Brunswick which 

 Prof. Duncan examined, and he has therefore palpably made 

 a very serious error of observation, owing to which his im- 

 portant argument for the original calcareous nature of lEndia 

 at once collapses; for as he states* that the Palceaclilya 

 •perforans only inhabits calcareous structures, then the tubes 

 or "threads in tliis siliceous material cannot be due to this 

 organism. 



But Prof. Duncan further states that the Palceaclilya has 

 perforated the calcareous spicules of Hindia as well as bored 

 through the infilling matrix, which, as we have just shown, 

 is siliceous. If this were the case it would indicate a marvel- 

 lous capacity of penetration in this lowly organism, to be 

 able to make its way directly through both calcite and silica 

 indiscriminately. But in this matter also there seems to be 

 another error of observation on Prof. Duncan's part, to which 

 Dr. Eauff first called my attention. After careful examina- 

 tion of the so-called tubes or borings of Palceachlya in New 

 Brunswick specimens, Dr. Banff failed to find a single instance 

 in which they passed through tlie spicules of the sponge. 

 They can be seen in microscopic sections to pass over and 

 under them in close proximity, but not through them. My 

 own observations confirm those of Dr. Banff. It would thus 

 appear that the action of the supposed Falieacldya 2^e,rforans 

 in the New Brunswick specimens of Hindia has been the 

 reverse of what, according to Prof. Duncan, it should have 

 been ; for instead of penetrating calcareous structures exclu- 

 sively, and eschewing the siliceous, it has left the calcareous 

 spicules of the sponge intact, and bored only into the siliceous 

 matrix ! 



There is, liowever, yet another point respecting this Palce- 

 achlya 2)erforans which requires explanation. Prof. Duncan 

 asserts that it carried on its borings " during the lifetime of 

 the organism," i. e. the sponge ; but in this case the canals 

 during the lifetime of the sponge were mere open tubes, and 



• Though Prof. Duncan reasserts in September 1886 what he stated 

 in 1879, that no long tubular vegetable structures with organs of repro- 

 duction (\. Q. Pcdceachhja pcrforans) have ever been found ramifjiug in 

 siliceous skeletons, yet in 1881, in a paper " On some remarkable Enlarge- 

 ments of the Axial Canals of Spouge-spicules and their Causes," pub- 

 lished in the Journ. Microsc. Soc, he v\rites that he agrees with Mr. 

 Carter that the perforations in the siliceous spicules of recent sponges are 

 produced by somewhat similar organisms to Palceachlya j)erforans (p. 568), 

 and he also finds zoospores in these perforated siliceous spicules singu- 

 larly resembling those of Achlya perfomns. 



