Pomona College, Claremont, California 163 
change occurs. It now begins to grow at such a rate as to almost 
double its size within twenty-four hours. The host, which here- 
tofore has betrayed no marked injury from its enemy, now rapidly 
shrivels up. Only five days of this voracious feeding reduces the 
once large plump larva to an empty skin and in its place we find 
the equally large and plump, fully grown larva of the bombyliid 
(Figs. 3 and 4). This long retarded growth followed near the 
end of the larval period by a relatively short period of unusually 
rapid development seems to be a very advantageous adaptation on 
the part of the parasite. If growth had progressed steadily from 
the first, death of the host had surely resulted before the full devel- 
opment of the parasitic larva. This larva now rests almost motion- 
less for ten or twelve days (Fig. 4) when it becomes a little more 
active and moults about two days later, entering the pupa stage 
(Fig. 5). In this stage it remains for fifteen to twenty days and 
emerges as an adult (Fig. 10). 
The work of this parasite for the season in which it was studied 
was quite general, about ten per cent. of the cells examined being 
infected. So far as I observed, its work was also very equally dis- 
tributed—about half the broods showed one parasitized larva and 
in only one case was there more than one found in the same brood. 
Other parasites found were a phycitid moth and a tenebrionid 
beetle, both of which began their work upon the bee-bread and when 
that supply ran short devoured the young bees. These two para- 
sites would doubtless be much more destructive were orpifex a less 
careful workman; for I found that where cells prepared for study 
were not tightly sealed the pupe were in almost every case devoured. 
But where the partitions were left entirely intact and the glass cover 
glued on tightly I found only one case in which a cell was entered 
and in this case the tenebrionid bored through the partition to 
deposit eggs within the cell. In some cases I used bee-bread to paste 
the glass cover over the opened cells and in every such case these two 
parasites found their way in by feeding upon this material and 
without fail they devoured the pupe before they emerged. From 
* my examination of cells which had not been opened before the season 
of emergence I conclude that the injury of these parasites is slight 
except in case of defective construction of partitions. But they 
were found occasionally even in the normal brood cells. 
