CuNLiFFE (N.). Some Observations on the Biology and Structure of 



Orniihodorits mouhata, Murray, 

 NuTTALL (G. H. F.). A Note on the External Characters which serve 

 to differentiate the Sexes. — Parasitology, Cambridge, xiii, no. 4, 

 November 1921, pp. 327-347, 1 plate, 5 figs. 



The observations recorded in this paper were made in 1913-14 in 

 continuance of an investigation begun by the late Mr. Gordon Merriman. 

 Very little information was available regarding the biology of Orni- 

 ihodorits moubata ; the present study was made to determine the number 

 of moults before and after reaching maturit}^ the changes taking place 

 in the external anatomy of the ticks at each stage of development, 

 and the duration of the different stages at different temperatures. 

 Pairing was observed between individuals of the two species, 0. mou- 

 bata and 0. savignyi, the resulting eggs being infertile. There is no 

 e\'idence of parthenogenesis in 0. moubata, nor do the ticks undergo 

 ecdysis after reaching maturity. 



The influence of temperature on oviposition is very marked. An 

 increase of temperature of 8°C. [14° F.] from 22° C. [72° F.] doubles the 

 rate of o\'iposition, but decreases the fertility of the eggs by 30 per cent. 

 It also reduces the longevity of the female tick from 715 to 397 days 

 {i.e., 40 per cent.), and approximately halves the period required for 

 metamorphosis under laboratorj^ conditions. Under these con- 

 ditions, at 37° C. [99° F.] reproduction ceases and the longevity of the 

 female is reduced by 80 per cent. From four to eight ecdyses may be 

 undergone before maturity is reached, the majority of males maturing 

 after the 5th ecdysis, and the females about equally after the 5th and 

 6th ecdyses. Engorgement can take place one or two days after 

 emergence at any stage except the larval, the average time required 

 being about three-quarters of an hour. The extent of engorgement 

 at each stage varies, but is not correlated with the ecdysis period. 

 Excessive moisture does not retard ecdysis, but is decidedly unfavour- 

 able to vitality, only one tick passing the 3rd nymphal stage under 

 these conditions. This result is of particular interest in relation to 

 Rodhain's observations on the distribution of 0. moubata in tropical 

 Africa [R.A.E., B, vii, 151]. 



A study of the structure of the hypostome, leg and spiracle leads to an 

 approximate determination of the stage of development attained. 

 The larval and first four nymphal stages are fairly well differentiated, 

 much more so than the later stages, but variation due to nutrition 

 requires further study. 



MacGregor (M. E.). The Influence of the Hydrogen-Ion Concen- 

 tration in the Development of Mosquito Larvae. (Preliminary 



Contribution.)— Pflras//o/o^y, Cambridge, xiii, no. 4, November 

 1921, pp. 348-351. 



As a result of experiment and investigation, the author concludes 

 that the frequent failure of mosquito larvae to develop normally under 

 laboratory conditions is largely due to changes in the hydrogen-ion 

 concentration, which evidently has a great effect on metabolism 

 of the larvae and their resistance to disease. It may, therefore, be 

 possible to combat mosquito development by making the water of 

 ponds acid and of tree-holes alkaline. Such methods would naturally 

 have a limited practical application. Further investigations are 

 proceeding. 



(5610) Wt. r.3/184 1500 2/22 Harrow G.753. C 



