142 MISSOURI BOTANICAL GARDEN. 
dinide, are more noticeable than in any other Lepidopteron, 
and while careful study shows them to be superficial and 
hardly homologous with the cencri they would seem to 
have some similar raison d’etre.* The broad and deep 
‘insertion between thorax and abdomen, with its contrasting 
coloring, also serves to increase the general likeness. 
Though I had briefly visited the tree Yuccas ( Y. brevi- 
folia) of the Mojave desert, in March, 1887, it was not 
until April 14th, of the same year, that I was able to spend 
a whole day among them, mostly in the Antelope Valley. 
There were but few specimens in bloom, but a number 
showed the old fruit, and it was with no little satisfaction 
that in almost every case I found that this indicated 
the presence of some Pronuba of a relatively large 
species, as evidenced by the holes of exit of the larva. 
The flower has the perianth very dense, the petals thick, 
fleshy, almost leathery, curved in at the tips, the bracts 
large and tough. Mr. Koebele was with me at the time, 
also Mr. Frank Godey and Mr. J. G. Wickersham. On 
account of the scarcity of the flowers, and the difficulty 
of reaching them without disturbing the moths, but 
two specimens of this Pronuba were obtained; but the 
small white Prodoxus sordidus was abundant in the 
flowers and its work everywhere noticeable in the 
flower-stems. From the fact that I could not be 
among those curious Yuccas at night, I was unable to 
witness the acts either of pollination or of oviposition 
of its particular Pronuba. The structure and characteris- 
* The structure and function of these cencri spots in Hymenoptera 
seem to be little understood. They vary instructure in different families, 
but for the most part consist of a membrane or lid which covers a cav- 
ity and suggests that they are sound-producing organs. In Lepidoptera 
the similarly placed, but superficial spots, are not specialized, but mere 
inflations or modifications of the chitine wall. They are wanting in the 
Rhopalocera and higher groups of Heterocera, while in the Tortricina and 
Tineina, in which they are usually well developed, they have remained 
unnoticed because usually hidden by the vestiture, or not conspicuous, 
through lack of contrasting coloring. 
