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XVII. The relation between the secondary sexual characters 

 and the Gonads and accessory sexual glands in 

 Insects. By E. A. Cockayne, M. A., D.M., F.R.C.P. 



[Read November 15th, 1916.] 



The remarkable effects of the secretions of the ductless 

 glands on the development of the secondary sexual charac- 

 ters in the vertebrates makes it of great interest to examine 

 the evidence for and against the existence of a similar 

 relationship in insects. In mammals and birds we know 

 that in the male the interstitial cells, or cells of Leydig, 

 which lie between the seminiferous tubules of the testis, 

 produce a secretion which causes the normal development 

 of the secondary sexual characters in the male at puberty. 

 Removal of the testes before puberty prevents their 

 appearance, but atrophy of the seminiferous tubules in 

 no way affects them. The testis is a double organ, each 

 part having its own distinct function. In the ovary a 

 similar state of affairs appears to exist, but has not been 

 so clearly demonstrated. 



Besides this comparatively simple relationship between 

 the interstitial glandular part of the gonads and the 

 secondary sexual characters, the ductless glands exert an 

 influence upon one another. For instance, over-activity 

 of the cortex of the suprarenal gland produces sexual 

 precocity, under-activity of the pineal body produces a 

 similar effect; but under-activity of the pituitary body 

 delays the appearance of secondary sexual characters. 

 These stimulating or restraining effects seem to be due to 

 the action of the internal secretions of these glands on the 

 gonads, causing an increase or decrease in the secretion 

 of the interstitial cells, and so only indirectly hastening 

 or retarding the appearance of secondary sexual characters. 



But it must be remembered that long before these cells 

 become active we find well-marked differences in the two 

 sexes, and such differences still remain if the cells be 

 removed and are present even in cases where the gonads 

 have never developed at all. It is only some of the more 

 striking differences, which appear at the time of puberty, 

 and which are due to the activity of the gonads. 



TRANS. ENT. SOC. LOND. 1916. — PARTS III, IV. (APRIL '17) 



