en. x.] 18431858. 185 



G, D. to L. Jenyns* Down, Oct. 12th [1845]. 



My dear Jenyxs Thanks for your note. I am sorry 

 to say I have not even the tail-end of a fact in English Zo- 

 ology to communicate. I have found that even trifling 

 observations require, in my case, some leisure and energy, 

 [of] both of which ingredients I have had none to spare, as 

 writing my Geology thoroughly expends both. I had always 

 thought that I would keep a journal and record everything, 

 but in the way I now live I find I observe nothing to record. 

 Looking after my garden aud trees, and occasionally a very 

 little walk in an idle frame of my mind, fills up every after- 

 noon in the same manner. I am surprised that with all 

 your parish affairs, you have had time to do all that which 

 you have done. I shall be very glad to see your little work \ 

 (and proud should I have been if I could have added a single 

 fact to it). My work on the species question has impressed 

 me very forcibly with the importance of all such works as 

 your intended one, containing what people are pleased gen- 

 erally to call trifling facts. These are the facts which make 

 one understand the working or economy of nature. There 

 is one subject, on which I am very curious, and which per- 

 haps you may throw some light on, if you have ever thought 

 on it ; namely, what are the checks and what the periods of 

 life by which the increase of any given species is limited. 

 Just calculate the increase of any bird, if you assume that 

 only half the young are reared, and these breed : within the 

 natural (i.e. if free from accidents) life of the parents the 

 number of individuals will become enormous, and I have 

 been much surprised to think how great destruction must 

 annually or occasionally be falling on every species, yet the 

 means and period of such destruction are scarcely perceived 

 by us. 



I have continued steadily reading and collecting facts on 

 variation of domestic animals and plants, and on the ques- 

 tion of what are species. I have a grand body of facts, and 

 I think I can draw some sound conclusions. The general 

 conclusions at which I have slowly been driven from a di- 



* Rev. L. Blomefield. 



+ Mr. Jenyns' Observations in Natural History. It is prefaced by an In- 

 troduction on " Habits of observing as connected with the study of Natural 

 History," and followed by a " Calendar of Periodic Phenomena inlSatural 

 History," with " Remarks on the importance of such Registers." 



