422 SUMMARY OF CURRENT RESEARCHES RELATING TO 



suppressed ; then ensues the period of growth. The first maturation- 

 division is a reduction-division ; the " accessory chromosome " passes 

 on undivided into one of the spermatocytes of the second order. The 

 centrosomes are V-shaped. The second maturation-division is an 

 equation-division. The " accessory chromosome " divides like the 

 other chromosomes ; the centrosomes are rod-shaped. Spermatids and 

 spermatozoa, with and without " accessory chromosomes," are indis- 

 tinguishable. Mitochondria arise from the chromatin substance of 

 the nucleus. They form the " Nebenkern " in the spermatids. The 

 " accessory chromosome " arises from the nucleolus, and must be looked 

 upon as a chromosome destined to perish. Eggs fertilised by sperma- 

 tozoa with an " accessory chromosome " yield females ; eggs fertilised by 

 spermatozoa without an " accessory chromosome " yield males. 



Behaviour of Young of Water Scorpion.*— S. J. Holmes has studied 

 the behaviour of the young of Randtra quadridentata Stal., which m 

 general appearance closely resemble the adults. Their movements are 

 very nearly the same as those of the mature insects. The young 

 Ranatra are exceedingly voracious, and are often cannibals. The food 

 consists mainly of small crustaceans and insects. A feeble phototaxis 

 is manifested the first day after hatching, and increases gradually as the 

 insect grows older. The death-feigning is not so decided or prolonged 

 as in the adults, and it differs in certain interesting particulars. The 

 young, like the mature forms, can be cut in two while in the death- 

 feint Avithout causing any response. 



It is difficult to understand how the death-feint in this species 

 can be of much value to it. The American species does not seem 

 to fly to lights, and even in the European Ranatra linearis this a rare 

 occurrence. The American species rarely leaves the water of its own 

 accord on any sort of inducement. " One is therefore strongly inclined 

 to believe that the death-feint, which is manifested only when the 

 insect is in the air, is rather an incidental result of certain physiological 

 peculiarities of the organism, than an instinct which has been built up 

 of natural selection for the benefit of the species." 



Similarly, it is difficult to account for the strong, and at times 

 almost violent phototaxis which Ranatra exhibits. In the air and near 

 a bright light Ranatra becomes, sooner or later, strongly positive, often 

 being wrought up to the highest pitch of excitement in its efforts to reach 

 the light. But the utility of this curious behaviour is quite obscure. 



" Accessory Chromosome " of Anasa tristis.t — Katherine Foot and 

 E. C. Strobell find that in the spermatogenesis of this form there is 

 no " accessory chromosome," no odd " heterotropic " chromosome ; that 

 the so-called " chromosome nucleolus " of the resting stage is the homo- 

 logue of the nucleolus of the egg ; that in its form and time of dis- 

 appearance it bears a striking resemblance to the plasmosome of the egg 

 of AUolohophora fcetida. 



New Parasites of Kermes.|— K. Sulc describes a peculiar rod-like 

 organism — Kerminirola kermesina g. et sp. n. — which he found in 



* Biol. Bulletin, xii. (1907) pp. 158-64. t Tom. cit., pp. 119-26. 



X SB. k. Bohm. Ges. Wiss., xix. (1906) pp. 1-6 (2 figs.). 



