410 SUMMARY OF CURRENT RESEARCHES RELATING TO 



that tlie connective will separate as two fine siliceous films in a 

 curved form, one belonging to one half of the frustule, the other to 

 the other half. 



In the case of a side view of a frustule in the process of division, 

 the two portions will separate at the extremities, expanding therefrom 

 in a curvilinear form. 



After a further time it will be seen that the portion of the 

 siliceous shell which contains the striation will be entirely separated 

 from the endochrome, and in many cases greatly curved. 



After the lapse of 24 or 36 hours, it will generally be noticed 

 that the siliceous portion containing the striation has broken up into 

 fragments which are exactly like the iron cramps of cariienters. In 

 fact, the striation is due to the juxtaposition of a number of these 

 little cramps along the length of the frustule, probably cemented 

 together originally. 



Synedra radians may be described as a long four-sided box, two of 

 the sides (top aud bottom) consisting of a siliceous film without any 

 markings, and the other two sides of a structure made up of cramps 

 holding the upper and lower side in position. 



Mr. Miiller adds : " I should have liked to illustrate this dis- 

 covery, but any one familiar with microscopical manipulation will be 

 able to see all that I have described better on the stage of the Micro- 

 scojie than in a drawing on paper. A power of 250 or 300 diameters 

 is sufficient for the observation. The success of the experiment 

 depends a great deal ui^on temperature, the purity of the potash, and 

 the condition of the diatoms. I can lay down no positive rule 

 regarding this, but can only recommend the experimenter to try again 

 when he fails in the fii'st essay." 



New Xanthidium.* — W. Archer notices a minute desmid of 

 rare occurrence ; one of those, in their way, interesting forms as to 

 which a decision is difficult as regards their generic position. When 

 met with on the few occasions on which he had detected it, though 

 .then in some quantity, he had marked the collecting-bottle " Acute- 

 angled Cosmarium " ; but, as a matter of fact, and taken strictly, the 

 form seemed to fit more properly in the genus Xanthidium. It is very 

 minute (about the size of Cosmarium tincium), semicells elliptico- 

 hexagonal, the aj^ices bearing at each side, and at the upper very 

 obtuse angles, a minute but very appreciable mucro, each front surface 

 of each semicell showing a distinct median jjapilla ; end view com- 

 pressed, showing at the middle on each side the very distinct and 

 prominent papilla. Thus the essentials of the genus Xanthidium 

 were fulfilled ; for, though the spines were reduced to a minimum, 

 they were there, albeit very minute and acute ; and whilst the con- 

 spicuous central boss or elevation, bordered by papillfe or ornamented 

 by scrobiculi of the larger forms, was reduced to a simple papilla, yet 

 it, too, was there. It is true that many minute forms, distinctly 

 Cosmaria, have a similar median papilla ; yet Mr. Archer would lean 

 to the view that, coupled therewith, the presence of the spinules at 



♦ Ann. and Mag. Nat. Hist., xi. (1883) pp. 285-6. 



