OF PERIODIC PHENOMENA. 359 



not in all cases in such exact accordance with nature 

 as more extended observation would make it. Also, 

 though the number of species (at least of plants) in 

 M. Quetelet's list is much greater than in the pre- 

 sent calendar, still, as this last is mainly intended 

 for English observers; and comprises most of the 

 species given by M. Quetelet which are found in 

 Britain, it may be of much collateral advantage in 

 this respect. 



(21.) The grounds of selection, in respect of the 

 phenomena registered in this calendar, are for the 

 most part similar to those already alluded to in the 

 case of the lists published by M. Quetelet. (15.) (17.) 

 Such as belong to the animal kingdom relate 

 principally to birds and insects. In the class of 

 birds, they are generally those which have a more 

 or less marked reference to, or connexion with, some 

 fixed period of the year, especially such as are cha- 

 racteristic of the season, and easily seized upon by 

 the observer. At the same time there are a few which, 

 without affording any particular indications of this 

 nature, may tend to illustrate and improve our 

 knowledge of the species to which they severally 

 relate. 



In the case of insects, nothing is noted, with a 

 few exceptions, but the time of their first appear- 

 ance. Of course, in this class, the list of species 

 inserted might be almost indefinitely extended. It 

 has been thought proper, however, to confine it, for 

 the most part, to such as are generally common and 

 well known, or which at least occur in greater or 

 less plenty each year in the neighbourhood in which 



