482 



Mr. Gr. Bidder. 



[May 12, 



This variation takes place, not only among closely allied species, but 

 in the granules of one and the same cell ; suggesting most strongly 

 that the substance itself is mutable, and that the different aspects it 

 presents are phases through all of which individual granules may pass. 

 Adding distilled water under the microscope to a fragment of white 

 Ascetta primordial™, all the granules turn orange-yellow (their colour 

 in the red variety), and the greater part of them can be seen instan- 

 taneously to dissolve. But in many of the cells there are a certain 

 number of granules which remain after a week's maceration, and then 

 exhibit considerable resistance to caustic potash ; in Ascandra reti- 

 culum the same phenomena occur with but slight variation.* In the 

 light of this history we may perhaps reconcile, on the one hand, 

 Ascetta clathrus, in which all the granules appear to be ultimately 

 dissolved in distilled water, and, on the other hand, Leucosolenia 

 cavata, in which Dendy finds them insoluble in boiling caustic 

 potash. 



I suggest as a working hypothesis that the yellow granules of Ascetta 

 clathrus are a soluble nitrogenous excretion which is highly mutable, 

 and readily gives rise to the less soluble substances occurring with it 

 in the granules of other Homoccela. I suggest that this substance is 

 probably the common nitrogenous secretion of the protoplasm in all 

 sponges, and that the horny sponges are those which have learned to 

 retain it within their bodies until it has formed one or other of those 

 more or less insoluble products which we usually recognise under the 

 hospitable name of spongin. I hope soon to discuss this hypothesis 

 more at length, and to give the full grounds for my conviction as to 

 the general presence in sponges of a glandular or flask-shaped external 

 ectoderm. 



The homology between cuticle and horn fibres has been insisted on 

 by Kolliker, 0. Schmidt, Hyatt, and others ; the resemblance between 

 dermal cells and spongoblasts has been noted by Marenzeller, and 

 emphasised by Lendenf eld ; their complete homology, and the proba- 

 bility of the slime of the skin being " spongin and much water," 



* If either of these two sponges be shaken violently for three minutes in dis- 

 tilled water, and the liquid thoroughly filtered, a clear yellow (golden-yellow 

 A. primordialis) slightly alkaline solution results. Acidifying with 1 part in 10,000 

 of acetic acid, there is no immediate effect; but in the course of some hours a 

 flocculent brown precipitate is thrown down, insoluble except on boiling, in either 

 concentrated caustic potash or nitric acid ; the solution made with boiling nitric 

 acid leaves a straw-coloured residue on evaporation which turns rich yellow on the 

 addition of ammonia, and becomes black on over-heating. I may note that I have 

 now (May 14) succeeded in obtaining crystals from a solution made by placing an 

 Ascetta clathrus in absolute alcohol ; after remaining some months in a bottle and 

 decreasing in volume, the alcohol contains a number of long, thin, glittering blade- 

 like crystals, as much as 3 mm. long, doubly refracting, very soluble in water ; the 

 nitrate appears to be soluble in nitric acid. 



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