242 Proceedings of the Royal Irish Academy. 
and only six in winter. The paucity of such observations during the 
winter may, however, be traceable to the fact that then, in conse- 
quence of the inclemency of the weather, fewer gatherings are made, 
than because the process of conjugation is of less frequent occurrence 
during the season. 
Classification. 
In the various systems of classification, the several authors have 
treated the facts they had to arrange as Procrustes is said to have dealt 
with his guests: ‘‘ Qui ad lectum hospites emensus breviores exten- 
debat longiores decurtabat.”” How just this observation is will be 
obvious if we consider Pfitzer’s fair criticisms on the anomalies of the 
systems of classification hitherto propounded. All systems are arti- 
ficial; and when we consider the immensity and variety of Nature’s 
productions, we cannot wonder if in every group some organisms will 
be found to exist which cannot, without violence, be reduced into the 
order proposed. Every plan of arrangement will be liable to objection; 
and that may be regarded as the best which is the most obvious, the 
most simple, the most comprehensive, and productive of the fewest 
anomalies. 
Pfitzer considers that the imperfections of the existing systems are 
traceable to the fact that the ground-plan has been laid down on a 
single line, and as a remedy suggests a system of classification based 
on several concurrent lines, the principal of which are the character 
and number of the endochrome-plates, the structure of the sporangia, 
and the symmetrical or unsymmetrical form of the frustules in their 
several aspects. Upon these lines Pfitzer has skilfully constructed a 
most ingenious system of arrangement; but however great its merits as 
a philosophical abstraction, it appears to me lable to objection on 
practical grounds. The dislocation of analogous species chargeable on 
former systems, so far from being avoided, is scarcely, if at all, di- 
minished by the proposed plan. Here we have the Nitzschiee brought 
into close contact with the Naviculez ; the symmetrical Synedriz and 
the unsymmetrical Eunotieze are placed side by side, and in near 
proximity to the Surirelleee. The symmetrical Fragilaries are severed 
from the symmetrical Synedrie, and associated with the unsymmetri- 
cal Meridiee. The Tabellariez are separated from the Fragilaries 
and ranged with the Lichmophoree. The character of the endo- 
chrome-plates seems to me a condition of too recondite a nature to 
admit of practical application; besides, the induction of facts on the 
subject is, as yet, far too limited to justify its adoption. As to the 
reproductive process and its results, if our knowledge on the subject 
were sufficiently comprehensive, it would furnish most valuable help 
towards the construction of a satisfactory arrangement of the Diato- 
macece ; but, unhappily, in the great dearth of authentic facts illustra- 
tive of the subject, we are not warranted in using the knowledge we 
have as a ground plan of a general systematic arrangement. 
