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206 thorax. When the bee walks about, the pollen-mass lies flat on the back and wings; but when the insect enters a female flower, always with the labellum turned upwards, the pollinium, which is hinged to the gland by elastic tissue, falls back by its own weight and rests on the anterior face of the column. When the insect returns backwards from the flower, the pollinia are caught by the upper margin of the stigmatic cavity, which projects a little beyond the face of the column; and if the gland be then detached from the back of the insect, or the tissues which connect the pollinia with the caudicle, or this with the gland, break, fecundation takes place." Dr. Crüger sent me specimens of the humble-bees which he caught gnawing the labellum, and these consist of Euglossa nov. spec., cajennensis and piliventris.

Catasetum mentosum and a Monachanthus, according to Fritz Müller, grow in the same district of South Brazil; and he easily succeeded in fertilising the latter with pollen from the former. The pollen-masses could be inserted only partially into the narrow stigmatic cleft; but when this was done, a process of deglutition, as described under Cirrhæa, commenced and was slowly completed. On the other hand, Fritz Müller entirely failed in his attempts to fertilise the flowers of this Catasetum with its own pollen or with that from another plant. The pollinia of the female Monachanthus are very small; the pollen-grains are variable both in size and shape; the anther never opens, and the pollen-masses are not attached to the caudicle. Nevertheless, when these rudimentary pollen-masses, which can never naturally be removed from their cells, were placed on the slightly viscid