THE AMERICAN 



MONTHLY 



MICROSCOPICAL JOURNAL 



Vol. IV. 



Boston, August, 1883. 



No. 8. 



The Pimctations of Diatoms. 



The observations of M. Prinz * differ 

 from the remarkable studies of Flogel, 

 O. Miiller and Green, in that those 

 observers do not admit that the inte- 

 rior layer of the valve is perforated. 



According to these cfbservers, the 

 valves completely separate the con- 

 tents of the cells from the exterior. 

 Miiller made his observations par- 

 ticularly on Triceratium favus, with 

 the aid of an ingenious method of sub- 

 mersion. In this species (and in 

 .many others similar to it, such as Bid- 

 dulphia reticulata^ and the triangular 

 form of that species common in the 

 Pacific Ocean), the inferior layer is 

 certainly covered with fine puncta- 

 tions disposed in radiating lines, which 

 do not fail on any part, and thus ex- 

 clude the presence of large openings. 

 It is true, one might admit that these 

 minute points correspond to small 

 canals traversing the inferior layer of 

 the valve. But I have examined very 

 large specimens of Triceratium favus, 

 var. septangularis, which possess an in- 

 ferior layer sufficiently thick to allow, 

 by changing the focus, the observation 

 of radiate punctations on the internal 

 face, and of short spines irregularly 

 distributed over the external face, sit- 

 uated at the base of the hexagonal 

 ^Iveoli ; the walls of the latter are 

 thick, and present spinous projections 

 at the angles. In Coscinodiscus struc- 

 tures analogous to those of Triceratium 

 favus are met with, and even Tricer- 



* Remarks of M. Grunow with reference 

 to the work of M. Prinz, translated and con- 

 densed from the Bulletin de la Soc. Beige de 

 Alicrosco/ie, 



atium consimile, Griin., very similar to 

 Triceratimn favus, possesses exactly 

 the structure of Cose, oculis-iridis, so 

 that the conclusions which apply to 

 one of these species may be well ex- 

 tended to the others. 



As concerns the Cose, ocu/is-iridis, 

 the inferior layer has circular depres- 

 sions and not perforations. The valve is 

 very thin in the depressions, so that 

 ebullition, or other violent treatment, 

 perforates them completely at these 

 points. But an irrefragable proof is 

 furnished by Cose, asteromphalus., so 

 closely allied to Cose, ocu/is-iridis that 

 it is often difficult to classify the inter- 

 mediate forms. In that the interior side 

 of the valves is covered with minute 

 points (depressions) disposed in such 

 a manner as to form upon the border 

 of- those depressed points, a crown of 

 large punctations becoming smaller 

 and smaller, and more difficult to ob- 

 serve, towards the centre, but always 

 covering the base of the depressions.- 

 By raising the lens out of focus these 

 minute punctations disappear, and in. 

 their place are seen the large circular 

 depressions, considered by M. Prinz as 

 perforations. Cose, gigas is also very 

 interesting. In it one only finds small 

 depressions in the middle ; toward the 

 border, these are surrounded by depres- 

 sions directed toward the exterior, so 

 that this species possesses at the centre 

 the structure of punctate forms, and at 

 the margin the structure of Cose, oeulis- 

 iridis, radiatus, and others similar. 



In Trinacria jRegina, it is true, the 

 depressions penetrate very deeply 

 toward the base, as in manv diatoms. 

 But at the bottom of these depressions 

 is found a smaller concavity, which, 



