478 SUMMARY OF CURRENT RESEARCHES RELATING TO 



immersion in petrol for one minute. The vapour kills all lice and nits 

 within half an hour. A solution (1 in 4) of petrol in vaseline is very- 

 effective in application to the human body. Benzine, toluene, and 

 acetone are at least as lethal as petrol ; they are, however, also very 

 inflammable. There is reason to believe that the insecticidal action of 

 the lower paraffins may depend on their greater diffusibility, and possibly 

 on their greater solvent action on some fatty or waxy substance in the 

 cuticle of the louse. 



Certain chlorine derivatives of methane, ethane, and ethylene are 

 more lethal to lice than any other substances as yet tried, and they are 

 non-inflammable. A 25 p.c. solution of dichlorethylene or trichlorethy- 

 lene in vaseline is very effective in application to the human skin. 

 Phenol disinfectants are not efficient unless the steeping tank be kept 

 at 65° C. Volatile oils have no direct insecticidal effect. Impregnating 

 garments with sulphur and the like is of little direct use. The louse can 

 feed through all sorts of ointments. The use of a petrol or benzene 

 bath is the main recommendation for clothes ; for the body, soaps con- 

 taining derivatives of ethane and ethylene, or trichlorethylene in vaseline, 

 or petrol in vaseline. 



Clover Pests.* — Giacomo del Guercio discusses a remarkable weaken- 

 ing and masking of Trifolium pratense observed in Italy during recent 

 years. The root system is attacked by Hylastes trifolii, the stems by 

 Apion virens, the flower-heads by Apion aprkans. Cecidomyid larva? 

 are also present, and the root system is furthermore attacked by Tylmchus 

 devastator, and less abundantly by species of Heterodera. Interesting 

 photographs are given showing the hardly recognizable appearance of 

 the infected plants. The infection is very fatal. 



7- Prototracheata. 



Distribution of Onychophora.f — Austin H. Clark has made a detailed 

 study of the distribution of the Onychophora. Although we have no 

 palaeontological evidence upon ivhich to base the conclusion, it would 

 appear that the Onychophora represent a very ancient type. Like most 

 ancient types (1) they are strictly nocturnal, (2) they are all built upon 

 the same plan with very little divergence from the mean, and (3) they 

 indicate land connexions which we know to have been very ancient. 



So far as we know, the Onychophora are confined within a relatively 

 narrow and circumscribed physical range ; that is, they require a fairly 

 uniform temperature within very moderate extremes, and a uniformly 

 high humidity. Although existing within very narrow physical limit, 

 they are in certain ways more independent of their immediate surround- 

 ings than the great majority of Invertebrates, for. they are predacious, 

 and apparently feed upon any organisms small enough for them to 

 overcome. 



The most striking feature of the geographical distribution of the 



* Rodia, x. (1915) pp. 235-301 (2 pis.). 



t Smithsonian Misc. Coll., lxv. (1915) pp. 1-25. 



