ZOOLOGY AND BOTANY, MICROSCOPY, ETC. Ill 



or terminal swellings of the filaments to be endowed with active 

 movement by means of a cilium. From the gonidia was developed an 

 irregular merismopodia-form, which soon passed into a zooglcea-like 

 mass, and finally into regular cylindrical tubes of different lengths. 

 The palmella-form described by Zopf he regards as a different organism 

 belonging to Ascococcus. The only remedy he believes to be filtering ; 

 but recommends that the water for the supply of large towns should 

 be obtained from deeper sources, and from springs free of salts of 

 ferrous oxide and far removed from industrial establishments. 



Alga parasitic on a Snake.* — P. Magnus describes, under the 

 name Cladopliora (^SpongommyJia) oioliioioliila, a fresh- water alga found 

 on the Siamese fresh-water snake, Herpeton tentaculatum. The dark- 

 green plant branches profusely, three branches nearly in one plane 

 springing from each node. From the lower cells of the main stem and 

 of the lower branches spring unicellular fibres, which serve as organs 

 of attachment, and enable the plant to resist the water through which 

 the snake swims. Associated with the CladopJiora is a characteristic 

 vegetation consisting of a number of diatoms, a Chayncesiphon and a 

 UlotJirix. 



Structure of Diatoms.f — M. W. Prrnz replies to the objections 

 made by Mr. Deby, Count Castracane, and Prof. A. Grunow (Vol. I. 



(1881) pp. 508 and 509, and II. (1882) p. 246), to his view of the 

 perforation of the valves of the species of diatoms examined by him 

 in thin rock sections. 



He considers that his objectors have drawn their principal argu- 

 ments from facts observed in different conditions and from the exami- 

 nation of species different from those which he described. He agrees, 

 however, that there are many species which present details of structure 

 which teach nothing in regard to the conformation of other species of 

 similar appearance. 



The details of the structure of Pleurosigma angulaium, for instance, 

 are too complicated and delicate to decide the question. The thinnest 

 sections of this species always comprise at least two rows of pearls or 

 pores. The siliceous membranes which contain these details will give 

 in section the image of two continuous lines, one inner and the other 

 outer. It is this which causes Dr. L. Flogel J to maintain the 

 existence of chambers closed by these membranes. This image is 

 produced with all the sections, even those of the large species ; but 

 this aspect disappears when the section is sufficiently thin and it is 

 examined by high powers. We then see that the black lines repre- 

 senting the membranes are discontinuous, and cut by bright lines 

 which correspond to the openings. To study these details the thin- 

 ness of the section must have relation to the fineness of the markings 

 to be resolved. The greater part of the beautiful work of Dr. Flogel 

 has been put in doubt by the observations of Muller,§ who has shown 



* SB. Ges. naturf. Freunde Berlin, June 20, 1882. See Bot. OentralbL, xii. 



(1882) p. 75. 



t Bull. Soc. Belg. Micr., ix. (1882) pp. 23-7. 

 i Arch. f. Mikr. Anat., vi. (1870) p. 472. 

 § Bot. Ztg., 1872, p. 242. 



