1885.] 



MICROSCOPICAL JOURNAL. 



53 



the observers of V. monilata were 

 not alone guilty of an oversight, for 

 in V. vestita there are also two con- 

 tractile vesicles. It then occurred to 

 me to repeat the examination of W 

 rhabdophora., described in The Mi- 

 croscope for February, 1885, and in 

 it also two pulsating vacuoles were 

 now observed. To have ovei'looked 

 them in this case is peculiarly annoy- 

 ing, for when the species was first 

 obtained from the vegetable infusion 

 where it appeared in abundance, this 

 possibility was borne in mind and the 

 double organ searched for. In all 

 these instances, however, the con- 

 tractile spaces are usually placed di- 

 rectlv opposite each other and, unless 

 the vorticella is in a certain position, 

 a single one only is visible as one ob- 

 scures the other, the lower being so 

 far bcN'ond the focus of the objective 

 that its pulsations are not noticeable. 



The presence of the double vesicles 

 is not only an interesting and import- 

 ant structural point, but it is especially 

 worth of note since the two have thus 

 far been observed only in such mem- 

 bers of the genus as possess some 

 form of cuticular investment, or of 

 surface ornamentation rather than 

 transverse striae, V'. vestita being 

 surrounded by a well-marked cellu- 

 lar coating, \^. rhabdophora having 

 an apparently mucilaginous covering 

 enclosing minute bacteriform bodies, 

 V. monilata^ as the name signifies, 

 bearing solid bead-like bosses over 

 its entire surface, and V. Lockwoodii 

 possessing similarly arranged but con- 

 spicuously nucleated cuticular eleva- 

 tions. As these species are appa- 

 rently more highly organized and 

 presumably somewhat higher in the 

 scale than are the smooth or simply 

 striated forms, so are they slightly 

 more complex in structure. 



Trenton, N. J. 



o 



A Growing Slide. 



Many are the working hints I re- 

 ceive from the columns of the Jour- 

 nal, yet, after all, I am often, like 

 every working microscopist, thrown 



upon my own resources. One of my 

 devices has proved to be so useful that 

 I will describe it. It is a growing 

 slide, made as follows : — Arrange the 

 specimen on an ordinary glass slide, 

 with a drop of water and cover-glass 

 as usual ; then confine the cover by 

 slipping a light rubber band over it 

 on the slide, and place the slide in a 

 dish of water of sufficient depth to 

 completely immerse the specimen. 

 In this simple manner I have kept 

 fresh-water algie for weeks in a grow- 

 ing condition, enabling me to observe 

 the process of conjugation from its 

 commencement to the final rupture 

 of the spores and formation of new 

 filaments. E. L. Cheeseman. 

 Knowlesville, N. Y. 



o 



Structure of Diatoms.* 



[23806.] — The daily-increasing 

 number of disputable or, at all events, 

 disputed questions connected with the 

 intimate structure of the diatom valve 

 and frustule will, I hope, be accepted 

 by your readers as a sufiicient reason 

 for the present attempt on my part to 

 determine the point raised by Dr. 

 Flogel, and answered in the negative 

 (erroneously in this instance, as I 

 venture to believe) by my valued cor- 

 respondent Mr. J. D. Cox, of Cin- 

 cinnati, Ohio. 



Flogel maintains, on the strength 

 of sections which I have seen antl 

 very carefully examined, in conjunc- 

 tion with these accompanying photo- 

 graphs, that in such genera as Tri- 

 ceratium and Coscinodiscus, the little 

 hexagonal or cylindrical cavities, 

 though completely closed by a sili- 

 cious film on the internal surface of 

 the^valve, are not closed by any such 

 membrane on the outer surface of the 

 valve. Mr. Cox, on the other hand, 

 strongly insists on the cellules being 

 closed by a silicious film externally 

 as well as internally. Of course, if 

 Mr. Cox's view be correct, we have 

 hereto deal with minute hermetically- 

 sealed cavities. 



Now, to my mind, the objections 



• From Eng'iish Michanic. 



