So narrow is the pass at this point that the efforts of the bee are distinctly manifest from the outside in the distension of the part and the consequent slight change in the droop of the lip. In another moment he has passed this ordeal, and his head is seen protruding from the window-like opening (A) on one side of the column. But his struggles are not yet ended, for his egress is still slightly checked by the narrow dimensions of the opening, and also by the detention of the anther, which his thorax has now encountered. A strange etiquette this of the cypripedium, which speeds its parting guest with a sticky plaster smeared all over its back. As the insect works its way beneath the viscid contact, the anther is seen to be drawn outward upon its hinge, and its yellow contents are spread upon the insect's back (Fig. 18 C), verily like a plaster. Catching our bee before he has a chance to escape with his generous floral compliments, we unceremoniously introduce him into another cypripedium blossom, to which, if he were more obliging, he would naturally fly. He loses no time in profiting by his past experience, and is quickly creeping the gantlet, as it were, or braving the needle's eye of this narrow passage. His pollen-smeared thorax is soon crowding beneath the overhanging stigma again, whose forward-pointed papillae scrape off a portion of it (Fig. 18 B), thus insuring the cross-fertilizing of the flower, the bee receiving a fresh effusion of cypripedium compliments piled upon the first as he says "good-bye." It is doubtful whether in his natural life he ever fully effaces the telltale effects of this demonstrative _au revoir_. [Illustration: Fig. 18 A] Such, with slight modifications, is the plan evolved by the whole cypripedium tribe. Darwin mentions bees as the implied fertilizers, and doubtless many of the smaller bees do effect cross-fertilization in the smaller species. But the more ample passage in acaule would suggest the medium-sized Bombus as better adapted--as the experiment herewith pictured from my own experience many times would seem to verify, while a honey-bee introduced into the flower failed to fulfil the demonstration, emerging at the little doorway above without a sign of the cordial parting token. [Illustration: Fig. 18 B] Occasionally I suppose a fool bumblebee is entrapped within the petal bower and fails to find the proper exit, or it may be--much less a fool--having run the gantlet once too often, decides to escape the ordeal; hence the occasional mutilated blossom already described.