42 PROCEEDINGS OF SOCIETIES. 



Mr. Stephenson then read a paper entitled " Observations on tlie 

 Inner and Outer Layers of Coscinodiscus when examined in Bisulphide 

 of Carbon and in Air." The paper was illustrated by drawings made 

 and enlarged upon the blackboard by Mr. Charles Stewart, and by 

 mounted specimens exhibited under the binocular microscope. The 

 paper will be found at page 1. 



A vote of thanks to Mr. Stephenson for his paper was proposed by 

 the President, and carried unanimously. 



Mr. Slack said that whilst he agreed generally with all that Mr. 

 Stephenson had said upon the subject, he thought that Mr. Stephenson 

 would hardly disagree with him in expressing his impression that the 

 hexagonal framework of this diatom was composed of beads. He had 

 carefully examined these aj)pearances, and could find no reason for 

 supposing them to be spurious. It might not j^erhaps be well known 

 that they could be shown by a first-rate ^-inch objective cut down to 

 an angle of 65'', and illuminated with a large condenser having a 

 central stop so as to give dark-groimd illumination. A good objective 

 used in this way would work well, even with a D or an F eye-piece, 

 and this view of the diatoms was a very instructive one. Having 

 viewed Coscinodiscus in this way, he also looked at it with a fine 

 ^-inch immersion, by Powell and Lealand, with various eye-pieces, the 

 result being that he had very little doubt but that the hexagonal frame- 

 work on its upper surface was really composed of two or more rows of 

 beads, and he thought that if very great care were taken in the ex- 

 amination, the thicker portions of the inner layer would prove to be 

 beaded. In no fractured specimen which he examined could he get 

 any proof of the existence of a fractured portion of a membrane at the 

 spots where Mr. Stephenson considered there was a foramen. He had 

 tried to test this by means of polarized light ; by placing a polarizing 

 prism under the condenser, and using a tourmaline eye-piece, he 

 obtained plenty of light, but though a feeble polarizing effect was seen 

 in the framework of the hexagons, there was no indication of the 

 existence of any membrane. In Triceratium there was undoubtedly a 

 very decided floor to the depressions. If it should be finally decided 

 that any diatoms had foramina, they would have to be separated from 

 others and placed in a separate class by themselves, although it might 

 possibly be that want of sufficient power fails to reveal them in 

 all. It was curious that Mr. Kitten's paper should in some measure 

 bear upon the same subject. Mr. Stephenson's method of resolving 

 some of the difficulties was, he thought, a very admirable one, and if 

 the example now set were to be followed out it would do much towards 

 redeeming their characters as microscopists from the taunt that when 

 studying diatoms they spent their time in counting a lot of dots. 



Mr. Charles Stewart said that Mr. Slack had mentioned the jiro- 

 bability of the beaded structure of the thickened ring or margin of the 

 foramen ; he had himself seen something like it, but did not think the 

 appearance was so much like upstanding bosses, as it was like little 

 notches. An analogous structure might be noticed in the Polycistinte, 

 very many of which presented a number of notches at the margin 

 of the hole, a majority of them presenting the appearance of a curious 



