264 SUMMARY OF CURRENT RESEARCHES RELATING TO 



when it was at once seized and for a moment arrested. Two Naviculce 

 would cross eacli other, and the resultant action would be of an inter- 

 mediary or restraining character, and on suddenly relinquishing their 

 hold of each other they would separate with a bound. At another 

 time the motive action of a diatom was seen to be of a halting nature, 

 as if waiting to gather up its contractile organs before attempting any 

 advance." 



On the other hand. Dr. E. Van Ermengem * says that notwith- 

 standing the use of various colouring reagents (aniline colours, 

 hasmatoxyline, and carmine), also osmic acid in solution and vapour, 

 and absolute alcohol, homogeneous-immersion objectives of Zeiss 

 (l-18th in.) and Tolles, and Abbe and Powell condensers, he has 

 not been able to find the least trace of any kind of locomotor organs. 

 The large species of Pinnularia, Pleurosigma, and Surirella which he 

 observed were in full vitality and moved very actively. The frustules 

 always seemed to him to move in an automatic manner as if they were 

 impelled by a blind force, very different from the impulsive sponta- 

 neousness which seemed to animate the different Protozoa by which 

 they were accompanied. A number of the diatoms had on their 

 surface immovable filaments which were more or less slender, and 

 strongly refracting — true epiphytes (Leptothrix) the nature of which 

 it was difficult not to recognize. 



Dr. Van Ermengem considers that there only remains to explain 

 the motions of diatoms the hypothesis which attributes them to the 

 action of purely mechanical forces, thermo-dynamical, and perhaps 

 of electro-capillarity. 



Markings of Diatoms.f — Mr. E. W. Burgess combats M. Prinz's 

 views as to the existence of openings, and says that " if we examine a 

 valve of Trinacria regina or T. excavata by direct light through the 

 valve, focussing sharply to the flat surface of the valve, we get to 

 the edge of the base of the areolae, and viewing the areola we find 

 that the colour is different to that of the field (outside the edge of the 

 valve), proving that we are looking through the substance of the areolae ; 

 and if the valve has its exterior towards the observer, we have to 

 withdraw the objective by the fine adjustment to reach the apex of the 

 areola ; and if the interior is towards us, we lower the objective by the 

 same means to reach the bottom of the pit or concavity of the areola. 



The same observations apply to the valves of Stictodiscus, Tri- 

 ceratium, and others. If these diatoms are viewed by reflected light 

 on a black background (if the valve has its exterior towards the ob- 

 server), the areolae catch the light, and would convince even the most 

 sceptical observer that they are not openings, but either pits or 

 spherules, such observations depending upon the side of the valve 

 towards the observer." 



♦ Report of Referee in Bull. See. Belg. Micr., ix. (1883) pp. 41-3. 

 t Microscopical News, iii. (1883) pp. 71-5 (8 figs.). 



