Besides, when we consider that the active life of these insects lasts hardly a month; when we remember that this period of activity is disturbed by dark, rainy or very windy days, during which all work is suspended; when lastly we ascertain, as I have done ad nauseam in the case of the Three-horned Osmia, the time required for building and victualling a cell, it becomes obvious that the total laying must be kept within narrow bounds and that the mother has no time to lose if she wishes to get fifteen cells satisfactorily built in three or four weeks interrupted by compulsory rests. I shall give some facts later which will dispel your doubts, if any remain. I assume, therefore, that a number of eggs bordering on fifteen represents the entire family of an Osmia, as it does of many other Bees. Let us consult some other complete series. Here are two: 1 2 3 4 5 6 7 8 9 10 11 12 13 F F M F M F M F F F F M F F M F F F M F F M F M In both cases, the laying is taken as complete, for the same reasons as above. We will end with some series that appear to me incomplete, in view of the small number of cells and the absence of any free space above the pile of cocoons: 1 2 3 4 5 6 7 8 M M F M M M M M M M F M F M M M F M F F M M M M M F M F F F F M M M F M These examples are more than sufficient. It is quite evident that the distribution of the sexes is not governed by any rule. All that I can say on consulting the whole of my notes, which contain a good many instances of complete layings--most of them, unfortunately, spoilt through gaps caused by parasites, the death of the larva, the failure of the egg to hatch and other accidents--all that I can say in general is that the complete series begins with females and nearly always ends with males. The incomplete series can teach us nothing in this respect, for they are only fragments starting we know not whence; and it is impossible to tell whether they should be ascribed to the beginning, to the end, or to an intermediate period of the laying. To sum up: in the laying of the Three-pronged Osmia, no order governs the succession of the sexes; only, the series has a marked tendency to begin with females and to finish with males. The brambles, in my district, harbour two other Osmiae, both of much smaller size: O. detrita, PEREZ, and O. parvula, DUF. The first is very common, the second very rare; and until now I have found only one of her nests, placed above a nest of O. detrita, in the same bramble. Here, instead of the lack of order in the distribution of the sexes which we find with O. tridentata, we have an order remarkable for consistency and simplicity. I have before me the list of the series of O. detrita collected last winter. Here are some of them: 1. A series of twelve: seven females, beginning with the bottom of the tunnel, and then five males. 2. A series of nine: three females first, then six males. 3. A series of eight: five females followed by three males.