1884.] 



MICROSCOPICAL JOURNAL. 



69 



find within the hexapfonal tracings : 

 1st, a narrow circle so thin as to be 

 scarce (listini^iiisliable in color from 

 the empty Held ; 2(1, another narrow 

 rinf;^ of pinkish color, evidently thicker 

 than the last ; 3d, another nearly col- 

 orless ring ; and lastly a small central 

 part of appreciably pink tint. Nearly 

 every broken valve will g^ive some ex- 

 amples of the inner lamina projecting 

 beyond the outer, and a patient ex- 

 amination will soon find examples in 

 which the fracture, passing through 

 the eye-spot so as to break ofVoidy an 

 outer segment of, say, one-third its 

 area, leaves the inmost spot, the pink 

 'pupil' of the eye, intact. I have 

 verified this so often as to be able to 

 assert it categorically. In a very re- 

 cent examination of the same material 

 I found a single instance in which a 

 crack from the interior of a valve 

 when both laminae were in place went 

 out through the inner plate where it 

 projected beyond the other, and dis- 

 tinctly ran halfway round the ' pupil ' 

 or central spot, and thence out to edge 

 of the plate. The view by transmitted 

 light, therefore, is consistent with and 

 corroborates that got by reflected light. 

 As to the upper film, the same 

 preparations give abundant evidence 

 of its existence, I have already re- 

 ferred to the fact that we sometimes 

 see in Isthmia the appearance of teeth 

 or notches about the edge of the areo- 

 he, which I have interpreted to be 

 little processes or buttresses running 

 forward from the thick walls to sup- 

 port the thin film of the areola. This 

 film in such cases will also show more 

 color in its central part, indicating 

 that the part adjoining the wall is 

 thinnest. These teeth have also been 

 noticed by difterent observers in large 

 specimens oi Coscinodiscus oculus iri- 

 dis, but in Peticolas's slides (what is 

 not* very common in other specimens 

 of the Nottingham earth which I have 

 seen) we frequently find this notching 

 of the outer film become a circlet of 

 large dots, twelve or more in number, 

 and within these a fainter dotting cov- 

 ering the whole area of the hexagon. 

 When seen in the whole valve this 



might be attributed to some diffrac- 

 tion eflect ; but here also patience has 

 proven the true solvent, and, after 

 careful search among broken valves, 

 I have found this film projecting be- 

 yond the edge of the broken walls be- 

 neath it, the larger circlet of dots 

 being plainly marked, the inner ones 

 very faint by central light, but show- 

 ing strongly with a little obliquity of 

 illumination. On such a valve you 

 may focus sharply upon the dotted 

 film, seeing nothing of the 'eye-spot' 

 in the lamina below ; then lowering 

 the objective you pass through its veil 

 and bring the lower plate with its 

 large circle into plain view. 



After becoming familiar with these 

 phenomena in the magnificent shells 

 of this deposit, it is not difficult to 

 trace the films which close the areolae 

 in other smaller forms of similar spe- 

 cies. In one or two instances I have 

 found little pillars or spines of silex 

 adhering to the inner lamina of the 

 shell, as if the hexagonal walls had 

 aborted, and the plates had been con- 

 nected by these pillars in a way simi- 

 lar to that figured by the Belgian 

 writers ; but that this is not common 

 is sufficiently attested by the hexag- 

 onal lines upon the inner plate as 

 commonly found, these lines being 

 the mark of fracture where the walls 

 have been separated from the plate 

 which caps them. 



( To be continued.) 



Styrax and Liquidamber as Sub- 

 stitutes for Canada Balsam. 



Dr. H. Van Heurck has published 

 an article upon this subject in the 

 Bulletin de la Soc. Beige de Micro- 

 scopies which should have been 

 noticed in these columns some time 

 ago. The matter has been held over 

 to enable the Editor make some prep- 

 arations with styrax, in order to sup- 

 plement the observations of Dr. Van 

 Heurck by a few of his own. Dr. 

 Van Heurck introduces the subject 

 with the following statement : "During 

 the month of May,* my friend. Prof. 



* This was in 1883.— Ed. 



