ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 857 



tlie sponge has its importance somewhat reduced by the uncertainty 

 which prevails as to the exact distribution of these compounds in the 

 living animal. A reserve of nutriment occurs at certain times in 

 several wide"*/ distinct spouges ; and in some cases starch has been 

 demonstrated between the cells, but there appears reason to regard 

 this as derived from algae. Oily matters have been extracted by 

 chemical processes from sundry sponges and traces of fatty matter 

 have been observed. Though so commonly found dissolved in fatty 

 matters in Yertebrata, colouring matters are found abundantly in 

 the sponges, although fats are so scanty in these organisms. They 

 occur in the endodermal ciliated cells {Spongelia clvara, Calci- 

 sponges) or in the mesoderm (Euspongia officinalis, Chondrosia). Some 

 forms (Calcarea) from being colourless take a brown colour when 

 placed in spirit, others [Suherites, Hircinia, and Stelletta, spp.) lose 

 their colour if exposed to the light. Aplysina aerophoha offers a 

 remarkable example of change of colour consequent on death, viz. 

 from a sulphur-yellow to prussian blue ; this is caused by changes in 

 certain roundish refractive mesodermal cells with bladder-like nucleus 

 and small surrounding granular space ; the colour is preserved un- 

 changed in solution of salicylic acid ; the substance which produces 

 it is considered to be reserve nutriment. The same body (aplysino- 

 fulvin) appears to occur in Aplysilla sp. and Hircinia sp., but changes 

 much less rapidly in Aplysilla than in Aplysina, perhaps because the 

 " reducing ferment " which hinders its conversion is decomposed more 

 slowly in the latter case. The Horny fibres have been shown to be 

 excreted from special mesodermal cells. No proofs have yet been 

 given of the occurrence of a moulding of the sponge-skeleton by 

 absorption, such as the plasticity of such forms as Ascetta clatJirus 

 would seem to suggest. In connection with the rearing of sponges it 

 is remarked that Cavolini's observation that after having taken root, 

 the pieces of sponge shed over the old parts a mucilaginous mass, in 

 which the skeleton subsequently appeared, might be utilized as giving 

 a hint where to look for the youngest parts, when these are sought 

 after, and thus further the study of tissue-development. 



Spermatogenesis in Sycandra. * — Although spermatozoa are 

 described in Calcisponges by both Hackel and Eimer, yet, as Dr. N. 

 Polejaeff points out, these authors are hopelessly at issue as to the struc- 

 tures which they thus describe, and their divergence leaves the matter 

 in as uncertain a condition as before. Carter's results are not more 

 satisfactory. Even Keller's and Vosmaer's alleged observation of these 

 structures cannot be regarded as conclusive. Polejaeff experimented 

 upon Sycandra raphanus at Triest, employing a large variety which 

 grows on posts in the harbour. Oblique sections of specimens 

 hardened in 0*01 to • 05 per cent, osmic acid solution, stained with 

 alum-carmine, showed large numbers of minute bodies deeply stained, 

 refracting light strongly ; these had previously been detected in 

 motion in sections from the living sponge ; sometimes they occurred 

 free in the radial tubes and intercanals, at others in roundish and 



* SB. Akad. Wiss. Wien, Ixxxvi (1883) pp. 276-98 (2 pis.). 

 Ser. 2.— Vol. III. 3 M 



