242 Proceedings of the Royal Irish Academy. 



and only six in winter. Tlie paucity of such observations during tlie 

 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 liable 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 Mtzschiese brought 

 into close contact with the JSTaviculese ; the symmetrical Synedrise and 

 the unsymmetrical Eunotiese are placed side by side, and in near 

 proximity to the Surirellese. The symmetrical Eragilarieae are severed 

 from the symmetrical Synedrise, and associated with the unsymmetri- 

 cal Meridiese. The Tabellarieee are separated from the Fragilariese 

 and ranged with the Lichmophoreae. 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 sufiiciently comprehensive, it would furnish most valuable help 

 towards the construction of a satisfactory arrangement of the Diato- 

 macese ; 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. 



