2 THE AMERICAN MONTHLY [January, 



on each valve. Nor do the valves separate along the raph^ or median 

 line, but along" the line of junction or suture. If the reader will turn 

 over a page or two to the conspectus, he will see it stated by II. L. 

 .Smith, of Tribe I, Raphidieai, for example : "' Frustules, mostly bacil- 

 lar in s. v., always with a distinct raphe on one or both valves^ 

 (Italics mine.) Thus the two statements do not agree, and that on p. 

 X will be likely to give the student a very different idea of what is meant 

 by the raphe.* But to return to our ai-ticle. 



The trouble has all come, in my opinion, from calling the inner poi*- 

 tion of the valve a hoop at all. For it suggests at once a barrel-hoop, 

 something which is free at both edges from that which it encloses ; 

 which is not usually the case with the diatom hoop, to say the least. It 

 is a misleading term, and is bound to confuse the student. It would 

 be much better, therefore, it seems to me, to drop it altogether, or 

 to speak of this piece as that portion of the membrane of each valve 

 which when separated from the valve has the shape of a hoop. For 

 as long as it is attached to the valve it is not a hoop, but the continua- 

 tion of the valve itself. Finding this portion, however, at times de- 

 tached, and shaped like a hoop, obsei'vers have thought there was only 

 one hoop to each frustule, and that it bound the two valves together, 

 whereas the truth is that there is a so-called hoop to each valve, and 

 the hoops found in settlings of the DiatomacetE did not come each from 

 a frustule but each from a valve, that is, two from each frustule. (There 

 may be a few exceptions, but in my opinion the above will hold as a 

 general statement.) 



Now, I am inclined to believe that very few amateurs have had the 

 occular demonstration of this fact. Having to write upon the subject, 

 and finding it impossible to reconcile the figures with what Carpenter 

 said, I went to my slides again, and with the binocular, and almost the 

 first peep at Isthmia showed me that the drawings were faulty in rep- 

 resenting the upper and lower edges of the two valves as continuous 

 lines instead of broken ones. And then I took down Schmidt's plates 

 and the whole thing was as clear as day. , And my advice to the student 

 is to do the same thing: to pick out all his slides of Isthmia., Biddul- 

 phia., and Triceratium., and using the binocular, look sharp at the up- 

 per and lower edges of the hoop, and he will soon see that each is not 

 one continuous line, but is formed by two lines, one of which is inside 

 the other. And then if he is fortunate he will find some frustules where 

 the valves have partly separated, and he will find that each valve has 

 its band or hoop, and that it forms one contmuous piece with the valve. 

 And when he has done this he will have done something that is better 

 than resolving AtttpJiipleura., for he will have gained a definite idea 

 of the structure of the diatom frustule. And this is a point that cannot 

 be too strongly insisted upon, since even the Micrographic Dictionary 

 has gone through edition after edition without stating or figuring the 

 matter correctly. 



The first thing then for the student to do is to get a correct idea of 

 the way the two valves are put together, and to do this he must not 

 rely upon the figures in the Micrographic or in Carpenter, but study 

 carefully the actual diatoms with the binocular. It will also be well 



* Since the above was put in type, Wolle has issued errata making the correction. 



