69 



for vegetation is very marked, being apparently due principally to the 

 protection it affords against wave motions. 



Development from egg to adult requires six to eight weeks. The 

 authors draw a distinction between generations and generation-periods, 

 the difference being that the latter are generations in which individuals 

 of the same age occur at the same time. It should be remembered 

 that the progeny of a given female may be of different ages, owing to 

 successive oviposition. In the Halle region several generations occur 

 in the year, but it is not possible to speak of generation-periods, as 

 larvae occurred at all times. It is probable that the absence of 

 generation-periods obtains in most regions. It has been assumed that 

 the spring and autumn peaks of the malaria curve indicate two definite 

 generation-periods of the mosquito, and that the difference of three or 

 four weeks between the malaria and mosquito curves represents the 

 development of the plasmodia in the mosquito plus the incubation 

 period. If, however, two generation-periods do not occur, this assump- 

 tion cannot be sustained, and Ziemann's explanation is probable, 

 namely, that the May rise in the malaria curve is due to relapses or 

 new infections in warm dwellings, and that the autumn peak results 

 from a maturing of the oocysts in warmth due to natural conditions 

 and not to artificial heating. 



Near Halle, as elsewhere in Germany, malaria was widespread in 

 the past. Its dechne is not due to lack of conditions favourable to 

 Anophelines or to circumstances unfavourable to plasmodial develop- 

 ment, but to improvements in agriculture and Hving conditions gener- 

 ally. There is, therefore, little danger of its increase, provided that the 

 unfavourable economic conditions due to the War are ameliorated. 



In the authors' experience the value of natural enemies of mosquito 

 larvae and pupae has been overestimated. Nor did they observe any 

 practical effect in connection with water-plants, such as Utricularia 

 vulgaris and duck-weed [Lemna]. 



The Bedbug : Its Relation to Public Health, its Habits and Life-history, 

 and Methods of Control. — Public Health Repts., Washington, 

 B.C., XXXV, no. 50, 10th December 1920, pp. 2964-2970. 

 [Received 9th February 1921.] 



The information given in this article has already been noticed 

 [R.A.E., B, V, 48]. 



Young (A. R.). The Cattle-tick and its Control. — New Zealand 

 Jl. Agric, Wellington, xxi, no. 6, 20th December 1920, pp. 

 318-323, 3 figs. 



Most of the information on Haemaphysalis hispinosa contained in 

 this paper has been noticed elsewhere [R.A.E., B, vi, 115; viii, 

 34, 206]. 



IvERsoN (J. P.). Annual Report of the Division of Animal Industry, 

 1919-20.— A///z/v. Bull. Cal. Dept. Agric, Sacramento, ix, no. 

 10-11, October-November 1920, pp. 503-520, 8 figs. [Received 

 10th February 1921.] 



Measures for the extermination of the Texas fever tick, Boophilus 

 {Margaropus)annulatus, are enforced by law in California. Dipping 



