;«OOLOGY AND BOTANY, MICROSCOPY, KTC. 509 



capillarity) between all the siliceous globules, but never penetrating 

 them, as it must if there were perfoi'ations. 



In a number of genera the valves are formed of two superposed 

 layers, and in this case it often haj^pens that the internal layer is 

 perforated by numerous orifices more or less circular, but these, 

 Mr. Deby is certain, do not perforate the external valve. 



Dr. L. Flogel intends to make a further series of sections of 

 diatoms by the microtome of his invention, by which he has been able 

 to make 150 consecutive sections of the brain of the cockroach. These 

 sections will probably decide the question of orifices. 



Count Castracane also discusses * the question, and reiterates his 

 opinion that the supposed orifices in P. angulatum are raised granules. 

 This is in accordance with the view of Dr. Wallich, and his observa- 

 tions on the action of moisture introduced among diatoms mounted 

 . dry. He considers, therefore, that the microphotographs of C. 

 Giinther are not correct, in so far as they show openings, and he is 

 confirmed in this view by his own experience with microphotography. 

 In order to eliminate a source of error in the Microscope, by which 

 concavities are shown where convexities really exist, and vice versa, the 

 Count has recourse to binocular stereoscopic vision, examining a 

 diatom under two different aspects. Thus Craspedodiscus micro- 

 discus magnified 535 times invariably appears with the markings in 

 distinct relief. 



Moreover, the sections of P. angidatum and P. halticum, which 

 M. Flogel succeeded in making some years ago,t showed clearly that 

 small interstitial cells existed in the thickness of the valve corre- 

 sponding to the elevated granules, so that orifices cannot, he considers, 

 exist. 



Movements and Vegetative Reproduction of Diatoms.^ — Eecent 

 investigations of E. Hallier on the Diatomaccfe have been directed 

 chiefly to the phenomena of cell-division and to the nature and cause 

 of their peculiar movements. 



He asserts that the processes of cell-division take place in exactly 

 the same way as in many other algee. That, for example, in Melosira 

 closely resembles those which Pringsheim describes in CEdogonium, 

 while the course is still simpler in Navicula, Frustulia, Surirella, and 

 other boat-like forms. This, he considers, disposes of the " box- 

 hypothesis," which always presented much that was improbable. No 

 indication of the formation of boxes is presented with a magnifying 

 power of nearly 2000; while the process of division can be seen 

 completed in a very simple fashion. 



The more ordinary theory of the cause of the movements of diatoms 

 is that they are due to the rotation of the protoplasm, which projects 

 slightly through a crevice in the front. No trace, howevei*, of such a 

 crevice can be detected by the objective mentioned ; while it is easily 

 seen that the movement is far too complicated for so simple a cou- 



* Bull. Soc. Belg. Micr., vii. (1881) pp. Ixxxvi.-ix. 

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



i Hallier, E., ' Unters. lib. DiatomeeB ; insbesondere lib. ilire Bewegungen u. 

 ihre vegetative Fortpflanzung.' 32 pp., 2 pis. (8vo, Gera-Uuterniiiaus, 1880.) 

 Ser. 2.— Vol. I. 2 M 



