I have yet to say a few words on females laying male eggs only. M. Schirach supposes that one branch of their double ovary suffers some alteration. He seems to think that one of these branches contains the eggs of males, while the other has none but common eggs, and as he ascribes the inability of certain queens to lay the latter to some disease, his conjecture becomes very plausible. In fact, if the eggs of males and workers are indiscriminately mixed in both branches of the ovary, it appears at first sight that whatever cause acts on that organ, it should equally affect both species of eggs. If on the contrary, one branch is occupied by the eggs of drones only, and the other contains none but common eggs, we may conceive how disease affects the one, while the other remains untouched. Though this conjecture is probable, it is confuted by observation. We lately dissected queens, which laid none but male eggs, and found both branches of the ovary equally well expanded, and equally sound, if I may use the expression. The only difference that struck us was that in these two branches, the eggs were apparently not so close together as in the ovaries of queens laying both kinds of eggs. _PREGNY, 12. September 1791._ LETTER XIII. _ECONOMICAL CONSIDERATIONS ON BEES._ In this letter I shall treat of the advantages that may be derived from the new invented hives, called _book_ or _leaf_ hives, in promoting the _economical knowledge_ of bees. It is needless to relate the different methods hitherto employed in forcing bees to yield up a portion of their honey and wax; all resemble each other in being cruel and ill understood. It is evident, when bees are cultivated for the purpose of sharing the produce of their labours, we must endeavour to multiply them as much as the nature of the country admits; and consequently to regard their lives at the time we plunder them. Therefore it is an absurd custom to sacrifice whole hives to get at the riches they contain. The inhabitants of this country, who follow no other method, annually lose immense numbers of hives; and spring, being generally unfavourable to swarms, the loss is irreparable. I well know that at first they will not adopt any other method; they are too much attached to prejudices and old customs. But naturalists and intelligent cultivators of bees will be sensible of the utility of the method I propose; and if they apply it to use I hope their example will extend and perfect the culture of bees.