June, igoi.] • Smith : On Some Digger Bees. 61 



and digs other cells until the two or the five as the case may be are 

 completely surrounded by empty cells. At Fig, 21 (Plate IV), we 

 have a 5-cell cluster drawn from photograph which shows how such a 

 series is arranged. The five brood cells were capped and of course 

 the plaster could not get into them ; but it did get into the sur- 

 rounding air spaces, and when the cast was dug out the plaster prac- 

 tically inclosed the brood cells and their contents. The photograph 

 shows that the plaster broke down and distorted the narrow partitions 

 between the cells, two being run into one near the lateral running to 

 the main burrow. These marginal cells had been continued beneath 

 the brood cells, and the plaster has been trimmed away with a pen 

 knife to expose the cells. It will be readily seen that in this way the 

 casts preserved safely all the contents of the capped cells and we could 

 examine the clusters at our leisure and trim out the insides whenever 

 we wished ; usually this was part of the evening's work. 



The first pollen -loaded bee was seen May 24, by Mr. Brakeley. 

 Bees were yet coming out of winter quarters and beginning new bur- 

 rows on May 26th, though on the 28th some of the casts showed 

 three cell clusters. This shows the enormous activity of the insects, 

 the older series of which was now down from 28 to ;^^ inches only ten 

 days after the real beginning of the season. 



Specimens of bees taken from the new burrows May 25th, 26th and 

 27th reached me May 31st, and all of these were dissected. All were 

 females and in all the ovaries showed developing ova. Usually there 

 was a tolerably equal increase of size on both sides ; but in some cases 

 the ovary on one side was much larger than that on the other, due al- 

 ways to the fact that one egg was reaching maturity. The greatest 

 development was four on one side, a single one on the other, all of 

 about equal size. In this species there are 4 ovarian tubes, and in each 

 tube 2 cells or eggs that seem likely to develop. It seems thus as if 

 the insect might lay 16 eggs; but I doubt if any of them ever do 

 place so many. The greatest number of brood cells that we ever 

 found connected with any one cast, apparently placed by a single indi- 

 vidual, was 15 and I much doubt whether any bee ever fills more than 

 that. Six or seven filled cells to a single burrow is about an average, 

 quite a number containing only two. This was not due to interfer- 

 ference or incomplete work : such cases occurred constantly, of course ; 

 but we never counted them in our estimate. A cluster was complete 

 when the cells surrounding the brood cell or cells were continued be- 



