ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
79 
somewhat within the margin of the disc ; central portion of disc navi- 
culoid, depressed, its ends terminating in the spines ; striae radiate, 
moniliform, extending from the raphe to the margin of the valve. The 
author considers that the three described species should be reduced to 
one, B. Christiana, and that the nearest affinities of the genus are with 
Aulacodiscus and Eupodiscus, differing from them only in the presence 
of a raphe. He considers that it should be placed among the Crypto- 
raphidae in H. L. Smith’s classification, as an abnormal genus possessing 
a raphe or pseudo-raphe. Melonavicula appears, however, to enjoy 
priority as the generic name. 
/3. Schizomycetes. 
Formation of Nuclei and Spores in Bacteria.^ — Dr. P. Ernst has, 
by means of three quite different methods, demonstrated in a number of 
bacteria a new element, small granules which are most frequently seen 
when the bacj^eria are developing with difficulty or are about to sporulate. 
There is no constancy in the number of these granules, for there may 
be one or more. They stain blue-black in warm alkaline metliylen-blue 
and cold Bismarck-brown solution. Delafield’s hmmatoxylin stains them 
black-violet, and Platner’s nucleus-black blackish. 
The author believes that he has proved that these granules develope 
into spores, and therefore calls them sporogenous granules. 
As they did not under some conditions become stained with Neisser’s 
spore-stain, they are to be considered as being actually different from 
spores, although the predecessors of these. This view is further sup- 
ported by the fact that haematoxylin and Platner’s nucleus-black stain 
the granules, but not spores. In their earlier condition they are easily 
peptonized (3 hours in solution of pepsin 0-5, HCl O’ 2, HgO 100), but 
as they become older the greater is their resistance to digestion ; and 
this is complete when they have developed into spores. With raethyleu- 
blue-Bismarck-brown the sporogenous granules stain blue-black, the 
spores blue. All boiling fluids, including pure water, cause their dis- 
appearance. The granules are certainly not vacuoles, and do not consist 
of fat (insoluble in boiling ether), or of starch (do not stain with iodine). 
Relations of Purple Bacteria to Light. j* — The forms studied by 
Prof. T. W. Engelmann are well known, viz. Bacterium photometricum, 
roseo-persicinum, ruhescens, sulfuratum; Beggiatoaroseo-persicina ; Clathro- 
cystis roseo-persicina ; Monas Okeni, vinosa, Warmingi ; Ophidomonas 
sanguinea ; Bhahdomonas rosea ; Spirillum ruhrum, violaceum. All these 
are coloured more or less intensely by a red-purple matter diffused 
throughout the protoplasm, Bacteriopurpurin ; and their reaction to 
light is due entirely to this substance, and not to the presence or 
absence of sulphur or sulphuretted hydrogen. 
The influence of light on purple bacteria is shown very markedly by 
the production of various movements, according to the various species ; 
and the amount of these movements appears to vary directly as the 
* Zeitschr. f. Hygiene, v. (1888) 61 pp. (2 pis.); cf. Bot. Centralbl., xxxviii. 
(1889) p. 858. 
t Arch. Ne'erlaud. Sci. Exact, et Nat., xxiii. (1889) pp. 151-98. Cf. this 
Journal, 1888, p. 473. 
