26G THE ZOOLOGIST. 



therefore of great importance and abundance; but the rest of their 

 life-history is quite unknown. The relation of these bacteria to 

 the lupines, and their whole action, is still very little understood. 



As regards the animal kingdom, many of the most interesting 

 recent discoveries have been made with reference to the com- 

 monest species. Until within the last few years the male of the 

 Gallfly, which produces the common King Charles Oak-apple, 

 was unknown. It is now found that the species goes through a 

 sort of alternation of generations, the autumn brood being quite 

 different from that of the spring. 



In Bees and some allied insects it has recently been dis- 

 covered on what the sex of the young depends. They are almost 

 the only animals of which this can be said. 



So again in the case of Eels. It was long ago mentioned by 

 Aristotle that nobody knew how or where Eels bred, and certainly 

 no one had ever seen until in the last few years the egg of the 

 Eel, or the young Eel just emerged from the egg. It has now 

 been shown, mainly by the researches of Grassi, that the history 

 of the Eel is in fact the reverse of that of the Salmon. The 

 Salmon comes up into our rivers to breed; the Eel goes down 

 into the sea and breeds in water of great depth. 



All our ponds are rich in different species of Rotatoria, the 

 Common Rotifer itself being very abundant ; and yet I believe 

 up to the present time no male of the genera Philodina, Rotifer, 

 Calledina, or Aclmeta has yet been discovered. 



Many other similar instances might be mentioned. These 

 few, however, suffice to show how many interesting problems in 

 Natural History remain to be solved. 



