ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 613 



does not agree with the proposed identification of the sterile filaments of 

 Aphanizomenon with Oscillatoria Agardhii ; regarding the latter as an 

 entirely independent species. 



Herr W. Schmidle * adds to the list 3 now species, Lauterborniella 

 eleganlissima g. et sp. n., Schrcederia belonophora, and ffliabdoderma line- 

 are g. et sp. n. The following are the diagnoses of the new genera. 



Lauterhorniella. Ooenobes minute, flat, square, consisting of 4 cells 

 arranged in a cross and imbedded in mucilage ; cells round or sub- 

 cuneiform on a vertical view and furnished with a thick spine ; semi- 

 lunate and with two spines on a lateral view ; chlorophyllous contents 

 parietal, with a single pyrenoid ; propagation by cell-division in two 

 directions. 



ffliabdoderma. Cells 8-10 /x long, 2 /x broad ; contents aeruginous, 

 homogeneous ; enclosed in a very delicate membrane and a scarcely 

 visible mucilage, formed by transverse division ; rarely forming a few- 

 celled filament, more often membranaceous families, which are ulti- 

 mately curved. 



Cosmocladium saxon^U!!).! — Herr B. Schroeder has studied the 

 structure and development of this colonial desmid, especially in refer- 

 ence to the fine threads which connect the individual cells with ono 

 another. He regards these as having their origin in extra-cellular cyto- 

 plasm, being, in fact, analogous to the protoplasmic threads which so 

 commonly connect the cells of a tissue with one another. He has been 

 able to trace their origin to the sieve-like perforations in the cell-walls, 

 near the base of the cells. The investing gelatinous envelope has at 

 first a radial structure, and serves as a protection to the colony against 

 unfavourable external influences. The statement that it consists of a 

 double layer was not confirmed. 



Formation of Auxospores in Diatoms.:}: — Herr G. Karsteu has 

 studied the formation of auxospores, especially in the genera Cocconeis, 

 Surirella, and Cymatopleura. In relation to the four types already 

 established by the author,|| he still regards ffliabdonema arcuatum as 

 probably the primary form. The process in Type I. shows the genetic 

 connection between the formation of auxospores and ordinary cell- 

 division, as also the entire absence of sexuality in the archaic forms. 

 A passage to more complicated phenomena is seen in Achnanthes sub- 

 sessilis, where there is undoubted sexuality, though of a low order. A 

 more fully developed sexuality is exhibited by the majority of ground- 

 diatoms. Of the second type, characterised by the formation of two 

 auxospores, the author regards Synedra affinis and Bacillaria paradoxa 

 as reversions. In Type III. there is also a distinct sexuality. In 

 Cocconeis the sexual nucleus is the result of a single, in Surirella of 

 a double nuclear division. In the Tabellarieaa and in the entire mass of 

 centric species, forms may be recognised which have descended in direct 

 lines from the original form. 



Pores of Diatoms. § — Herr F. Schtitt regards the present position of 

 the question of the perforation of the diatom-valve to be somewhat as 



* Tom. cit.,p. 144-58 (1 pi.). t Tom. cit., pp. 15-23 (1 pi.). 



% Flora, lxxvii. (1900) pp. 253-83 (3 pis.) Cf. this Journal, ante, p. 491. 



§ Cf. this Journal, 1899, p. 514. 



f| Ber. Deutsch. Bot. Ges., xviii. (1900) pp. 202-16. Cf. this Journal, «nte,p.3C0. 



