510 SUMMARY OF CURRENT RESEARCHES RELATING TO 



trivance, which scarcely finds a parallel in the entire vegetable 

 kingdom. The causes of the movement are seen to reside in the 

 contractility of the entire young diatom-cell, closely resembling, 

 therefore, that of the Flagellate Infusoria. This result is of some 

 importance in relation to the theory of descent, indicating that 

 diatoms are in fact neither animals nor plants, or both at once, their 

 mode of nourishment, formation of auxospores, and mode of cell- 

 division associating them with the ConjugataB, while their movements 

 are those of the lower animals. With the exception of the Oscilla- 

 toriese, where the motion appears to be due to the same cause, a 

 movement of this peculiar kind of the entire vegetative cell-wall 

 scarcely recurs in the whole vegetable kingdom. 



The " box-hypothesis," and the ordinary theory of the movement 

 of diatoms, have been founded on the false premise of the absolute 

 rigidity of the "lorica" of the young diatom-cell. The complete 

 inaccuracy of this idea can, the author thinks, be easily proved. 



The instruments used by the author in his investigations are the 

 dry and the water-immersion systems L. and M. of Zeiss up to 2500 

 linear magnifying-power, as well as the ^ oil-immersion. As long 

 as it was possible, only low-power eye-pieces were used, although one 

 of the principal advantages of the oil-immersion system is that high- 

 power eye-pieces can be employed without injury to the clearness and 

 definition of tbe images. 



As a favourable instance of the formation of " boxes," should this 

 be a correct interpretation of the phenomena, the author took the 

 common Melosira varinns, in which the secondary side is as long 

 as possible ; — understanding by " primary side " (Hauptseite of 

 Eabenhorst) the side parallel to the plane of division ; by " secon- 

 dary side " {Nehenseite of Eabenhorst) the side at right angles to the 

 plane of division. Careful observations, however, did not give the 

 least sui:)port to the correctness of this hypothesis, the ditierence in 

 the size of the two daughter-cells which result from the cell-division 

 being due to differences in nutrition or in the other vital conditions. 

 A new formation of cell-wall (Hautungsprozess) takes place before 

 tlie division, and this is especitilly well seen in the foi-mation of 

 auxospores. In this process, by the formation of a cu'cular division 

 in the centre of the cell, the cell-wall is split into two cylinders, open 

 within and closed without, which then separate from one another by 

 the gradual expansion of the protoplasm. The further development 

 of the auxospore is then described in detail. Between tbe formation 

 of auxospores and the ordinary cell-division there is this difference, 

 that in the latter, before division, the cell which is thus split increases 

 to double its original length, so that each of the two newly formed 

 daughter-cells about equals the original mother-cell in length ; while 

 the auxospore considerably exceeds double the length of the mother-cell. 

 The author regards the formation of auxospores as an arrested process 

 of cell-division, or as a process of rejuvenescence. When the auxo- 

 spores are disposed in an isolated manner in an elongated vegetative 

 chain, their position is undetermined ; but when they lie one imme- 

 diately behind another in the chain, the anterior and posterior ends of 



