Removal of Corpora Allata on Egg Production in the Grasshopper,Melanoplus Differentialis. ∗

It has been shown by Wigglesworth 1 that in Rhodnius prolixus the corpora allata secrete a hormone which is necessary for the production of eggs. In order to determine whether these glands have a similar function in the grasshopper, females were operated as shown in Table I. For comparison, unoperated adults were killed at intervals from one to 42 days after moulting. Camera lucida drawings were made of the largest eggs in each of the above animals, egg length was measured, and the oviducts were examined to determine whether the secretion produced by the anterior portions of the oviducts was present. This secretion forms the ootheca.

There was great variation in the development of the ovary in unoperated adults autopsied from 28 to 42 days after moulting. However, of the 43 specimens examined, 35 contained eggs which were more than 1 mm. in length. Of these, the eggs of 8 were fully developed and had passed into the oviducts. The operated controls at autopsy also contained eggs exceeding 1 mm. in length and in one instance the fully developed eggs had entered the oviducts.

The eggs of the animals from which both corpora allata had been removed, however, were less than .9 mm. in length at autopsy in all cases except those which had been operated at 16 and 23 days, suggesting that development of the eggs was suppressed by lack of the corpora allata. The slightly larger size of the eggs in those animals operated at 16 and 23 days was probably because they had reached a higher stage of development before operation, since a number of unoperated females killed between 16 and 23 days were found to contain eggs exceeding .9 mm. in length.

At autopsy, secretion was lacking in the oviducts of all the animals operated up to 11 days after moulting. This indicates that formation of the secretion is also inhibited by removal of the corpora allata, since both the operated and unoperated controls, as well as the animal from which only one gland had been removed, contained secretion in the oviducts at autopsy, even in those cases where the eggs had remained small. Secretion had probably already started in the oviducts of the animals operated at 11, 14, and 23 days and had not in those operated at 13 and 16 days. This is evidenced by the fact that secretion had begun in some of the unoperated animals examined at from 10 to 23 days, while in others it had not.