578 SUMMARY OF CURRENT RESEARCHES RELATING TO 



case the oocytes degenerate, and the activity of the primordial female 

 cells is suspended ; the primordial male cells multiply and undergo 

 maturation. After the oocytes are advanced in the growth period, male 

 development is no longer possible. 



The nature of the stimulus to male development remains unknown. 



1. It depends upon the presence of the actual body of a large individual. 



2. The movement of the smaller individuals, from whatever cause, does 

 not furnish the stimulus, for some males are developed while in the 

 fixed position. 3. Male development does not depend upon the amount 

 of food received ; for starved neuter specimens develop a testis as 

 quickly as well-fed ones, when in the presence of large females ; and 

 they do not develop any more quickly. 4. No experiment has so far 

 demonstrated the existence of a stimulating secretion, but this possibility 

 has not been thoroughly tested. 5. The stimulus does not depend upon 

 the presence of the hermit-crab with which the molluscs are associated ; 

 it will have its effect even if the home of the colony is a finger-bowl. 



Whatever the nianner of working, the adaptation is advantageous. 

 For it provides that the male members of every colony shall quickly 

 develop into females as soon as there is no longer a larger female which 

 requires fertilization ; and also that there shall be adult males in the 

 colony ready to function as soon as any individual has reached the adult 

 female phase. 



Arthropoda. 



a. Insecta. 



Effect of X-rays on Length of Life of Flour Weevils.'' — Wheeler 

 P. Davy has experimented with the beetle Tribolium confusum, which 

 does much harm to cereal stuffs. It was found possible to destroy the 

 eggs of the beetle by using X-rays, and careful exclusion showed that 

 the lethal effect was due to the X-rays only, and not to some accidental 

 circumstance. 



Circulation of Blood in Insects.f — F. Brocher has made an 

 experimental study of the circulation of the blood in insects, using 

 chiefly fully developed specimens of Dytlcus margmah's and two species 

 of Odonate larvse. Most of the conclusions reached in this paper refer 

 to D. marginalis, and the experiments were especially directed towards 

 determining the function of the dorsal blood-vessel. The structure of 

 the vessel is not described in detail, but on two points the author 

 differs from Oberle ; he finds only seven pairs of ostia, not eight, and 

 he does not accept Oberle's statement that the dorsal vessel terminates 

 posteriorly in a cul-de-sac. The experiments showed that when Dyticus 

 is in a state of repose, as under an anaesthetic, the blood contained in its 

 abdomen is subjected to negative, not positive, pressure. This negative 

 pressure results from the action of the dorsal blood-vessel which, 

 pulsating continually, attracts to itself the liquid in the abdominal 

 cavity. In the dilated posterior portion of the vessel this inspiratory 



* Journ. Exper. ZooL, xxii. (1917) pp. 573-92 (5 figs.), 

 t Arch. Zool. Exper., Ivi. (1917) pp. 347-58. 



