ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 503 



(October 9, 1902) in an aquarium. Three days later the sponges were 

 dead, but gemmules had attached themselves to the glass walls and were 

 beginning to form new sponges. In twelve days the young sponge 

 grew to a size of 3 cm., and when eighteen days old it had a new 

 generation of gemmules. Microscopical examination showed that these 

 aquarium specimens differed a little from those in the river in respect 

 to the spinose rhabda around the gemmules. 



Siliceous Spicules.* — G. C. J. Vosmaer endeavours to introduce 

 some improvements in the classification of siliceous sponge spicules. 

 Thus in the group of monaxons, two fundamental divisions may be dis- 

 tinguished, according to the fact whether the ideal axis lies in a plane 

 or not. In the former case the line may be straight, curved, bent, &c. ; 

 in the latter case the line is a screw helix (approximately, as all vital 

 structures are). The spicules of the first set are called " pedinaxons" 

 those of the second " spir axons." And among the spiraxons we can 

 distinguish two sets : — (a) the screw line is formed on the surface of a 

 circular cylinder (a-spiraxons), or (b) on that of an elliptical cylinder 

 (/3-spiraxons), of large and small " pitch " respectively. The a-spiraxons 

 include sigmaspira, spirilla, spinispira, microspira, and sterrospira-types j 

 the /3-spiraxons include sigma, chela, and diancistra-types. 



Protozoa. 



Conjugation of Amosbse.| — Margherita T. Mengarini has described 

 what seem to be incontestable cases of the conjugation of two (or even 

 three) small forms (microgametes) of Amceha undulans to form a large 

 unit or macrogamete. 



Observations on Acanthometrea.f — W. Schewiakoff finds that the 

 acanthin skeleton consists of calcium-aluminium silicate (with traces of 

 iron), and is probably, in life, a hydrate of calcium-aluniinium-silicate. 

 This chemical composition makes it clear why there are no fossil remains 

 of Acanthometrea ; their fallen skeletons are dissolved in the sea- 

 water. 



Schewiakoff goes on to discuss the arrangement and fine structure 

 of the contractile elements or myonemes, &c, the changes associated 

 with their contraction and elongation, and the influence of various 

 stimuli — electrical and mechanical — on their excitability. 



Senescence and Conjugation in Infusorians. — G. Loisel maintains 

 that senescence in an Infusorian implies that in its vital reactions with 

 its environment, an increasing number of protoplasmic molecules are 

 put out of action (" se trouve immobilise ") either temporarily or per- 

 manently. Assimilation becomes increasingly difficult and there is a 

 progressive diminution in the power of natural immunisation. In- 

 jurious substances, injurious in the widest sense, accumulate and are 

 incompletely neutralised. 



On the other hand, conjugation is interpreted as implying a kind of 



* Proc. Section of Sci. k. Akad. Wetensckappen, Amsterdam, v. (1902) pp. 104-14. 

 t Atti R. Accad. Lincei (Rend.), xii. (1903) pp. 274-82 (4 figs.), 

 t Mem. Acad. Imp. Sci. St. Pe'tersbour?, xii. No. 10 (1902) pp. 1-40 (4 pis.). 

 § Zool. Anzeig., xxvi. (1903) pp. 484-95. 



