ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 615 



number of nuclei and chromatophores in growth and mature stages, the 

 presence of contractile vacuoles in the anterior and in the posterior ends 

 in the motile stage, the method of chromatophore division, and the absence 

 of such organs as pyrenoids, gullet, and stigma, makes its systematic 

 position rather difficult to determine. 



Asexual Mode of Auxospore Formation.*-- K. Yendo and K. 

 Akatsuka describe the mode of auxospore formation of Arachnoidiscus 

 Ehr&ribergii Bail. The spores were formed asexually, each from a single 

 frustule. In the essential points the process of formation accords satis- 

 factorily with that already observed by Smith, Schiitt, etc., for Melosira. 

 As, however, the process has not hitherto been known in Arachnoidiscus 

 Ehrenbergii, the authors give here an account of it. 



Physiology of Diatoms. f— 0. Richter, in a previous paper, showed 

 that sodium was indispensable to Nitzschia putrida Benecke, a marine 

 diatom, and in the present paper he shows that the same holds good for 

 brown marine diatoms of the Nitzschia and Navicula type. As a proof 

 of this he made use of a medium containing agar and 1 p.c. and 2 p.c. 

 of salts of sodium, magnesium, and potassium. He considers that the 

 membrane of marine diatoms contains sodium silicate. 



Diatoms of the Sedbergh District.^ — R. H. Philip publishes a short 

 study in the evolution of diatoms, founded on Peragallo's theory and 

 illustrated by his examination of the species in the Sedbergh district. 

 He shows first that diatoms are divided into three sub-families : the 

 Raphidieas, having a true raphe on at least one of the two valves ; the 

 Pseudo-Raphidieae, having a blank space simulating a raphe on at least 

 one valve ; and the Crypto-Raphidieas, which possess neither a true raphe 

 nor the appearance of one on either valve. The first division (with some 

 exceptions) are self-motile. The other two divisions are incapable of 

 self -movement. He then goes on to show that diatoms may be regarded 

 as being descended from a common ancestor with Radiolaria, an ancestor 

 in which the differentiation of animal and vegetable had not been attained. 

 In any case, however, the Diatoinaceae which are nearest to the Radio- 

 laria are the earliest to appear in fossil deposits. These all belong to 

 the Crypto-Raphidieae, or as Peragallo prefers to call them, the Ana- 

 Raphiclieae. As the life of diatoms devoid of power of motion was fraught 

 with danger from the continual deposition of silt and other causes, it is 

 evident that species which could develop a raphe and consequently a 

 power of motion, would greatly benefit in the struggle for existence. 

 Thus we find that the Raphidieae are much the largest of the sub-families 

 of to-day. Taking for instance the diatoms of the Hull district, of the 

 600 species recorded two-thirds are Raphidieas and less than a sixth 

 Ana-Raphidieae. The author then goes on to show how great an advan- 

 tage species of the Pseudo-Raphidieaa would have on the other hand in 

 the ghylls and streams of gorges ; and explains the acquisition of a stipes, 

 like that of Gomphonema, and the advantages to be gained by the forma- 

 % tion of chains, etc. He then details the species in the Sedbergh district, 



* Bot. Mag. Tokyo, xxiv. (1910) p. 47-50 (pi.). 



t SB. k. Akad. wiss. Wien., cxviii. (1909) pp. 1337-44. 



X NaturaMst, No. 639 (1910) pp. 148-52 (pi.). 



