392 



NATURE 



[June 



1910 



illustrated and described by Dr. Drake-Brockman. 

 He tells us some new things about the long-necked, 

 long-tailed dibatag (Ammodorcas) and gerenuk (Litho- 

 cranius), and about the oryx. In this last type (of 

 which the book gives an excellent photograph) the 

 reader is recalled to one of the problems of faunistic 

 geography as yet unsolved, i.e. why is there such a 

 strong affinity in mammalian and bird fauna, and to a 

 lesser extent in flora, between south-west and north- 

 east Africa, between Somaliland (in its largest geo- 

 graphical extent) and Trans-Zambezia ? The Beisa 

 oryx of north-east Africa and the Cape gemsbok are 

 more nearly allied than either is to the fringe-eared 

 oryx (O. callotis) of East Africa. In both north-east 

 and south-west Africa we have ostriches, aard-wolves, 

 otocyons, gazelles, foxes, black-backed jackals, secre- 

 tary birds, striped hyaenas, caracal lynxes, and 

 cheetahs. North of the Zambezi and the Zambezi- 

 Kunene line they do not exist, nor south of the Tana 

 River and the Anglo-German frontier in Masailand. 



There is even a slight correspondence (in these 

 geographical extremes of Africa) in the affinities of 

 the lowest human types. Linguistically, the only 

 allies of the south-west African Hottentots are in 

 equatorial German East Africa, and physically the 

 only resemblances to the Bushman are to be met with 

 in some of the Andorobo, Suk, and Doko helot tribes 

 of north-east Africa, north and east of Unyamwezi 

 and the Kilimanjaro district. Why should the 

 connecting links of so many mammal and bird types 

 have died out in between? The intervening regions 

 were almost certainly covered down to quite recent 

 times by dense forest, a forest only abated by the 

 Neolithic negro. How did the "desert" types referred 

 to of Somaliland and south-west Africa work their 

 way through this forest-land across many degrees 

 of latitude, and 3'et retain their peculiar adaptability 

 (in colour as well as peculiarities of hoof and habit) 

 for arid countries? A similar problem remains un- 

 solved in regard to South America, in the south- 

 western parts and southernmost extremity of which 

 continent there are mammals related to North 

 American types (such as Andean bear, the Antarctic 

 wolf, and the Auchenia camelids) the nearest affinities 

 of which are with North American forms, yet which 

 to reach their present habita.t must have traversed a 

 greater or less breadth of densely forested, steamingly 

 hot equatorial America. H. H. Johnston, 



SOME BRITISH FRESH-WATER PROTOZOA. 

 British Fresh-water Rhizopoda and Heliozoa. Vol. II. 

 Rhizopoda, Part II. By the late James Cash, 

 assisted by John Hopkinson. Pp. xviii+ 166 + 32 

 plates. (London : Ray Society, 1909.) Price 

 12s. 6d. net. 

 ' I 'HE appearance of the second volume of this useful 

 J- monograph of the British Rhizopoda was 

 heralded some few months ago by the sad announce- 

 ment of the death of the author, Mr. James Cash. 

 The descriptions of the species and the beautiful plates 

 which illustrate them were from the hand of the 

 devoted and enthusiastic Manchester microscopist, and 

 it will always be a matter for sincere regret that his 

 life was not spared to see the completion of his work. 

 NO. 21 18. VOL. 8^1 



I To Mr. John Hopkinson we are indebted for the notes 

 I on synonymy, for the bibliography, and for the 

 I responsibility of seeing the volume through >tlie press 

 after the death of Mr. Cash. 



The genera dealt with in the present volume are 

 those included in the divisions of the Conchulina 

 called by the authors the Difflugina and Nebelina. 

 This leaves the treatment of the testaceous forms with 

 filamentous pseudopodia and the Heliozoa to a third 

 volume. 



As pointed out in our review of the first volume 

 (May 17, 1906), this monograph is one that is essen- 

 tially systematic in its treatment. It includes the 

 description of a number of forms which are considered 

 by those who have made a special study of them to be 

 specifically distinct or to be racial varieties of distinct 

 species, but it does not attempt to deal with the more 

 difficult problems of life-history and the influence of 

 the environment. To the working microscopist who 

 is anxious to find names for the varieties he discovers 

 in the fresh-waters that he visits it will doubtless b< 

 of some value, for it gives him, in a convenient form 

 and with excellent illustrations, a statement of th« 

 names that have been given to the varieties oi 

 Difflugia, Lesquereusia, Quadrula, and other well 

 known genera. But a purely systematic work of this 

 kind cannot fail to raise in the mind of an inquire* 

 many interesting questions that it altogether fails t( 

 satisfy. For example, of the genus Difflugia alone 

 no fewer than twenty-three species are described, vary 

 ing in length from 15M to 250/*. Is there really any 

 satisfactory evidence to prove that the smaller forms 

 such as D. penardi and D. globulosa, are not th« 

 younger stages in the growth of the larger forms 2 

 In the closely allied genus Centropyxis, Schaudinn has 

 proved that the zygote formed by the fusion of a 

 megagamete and a microgamete forms a small shell, 

 but no one has, at present, described in detail the 

 characters of the shells of the different stages of 

 growth from the zygote until the full size of the adult 

 is attained. Until this has been carefully done by 

 the culture method, with two or three examples, the 

 real value of the specific characters used in systematic 

 treatises must be accepted with very great hesitation. 

 In the meantime, it might be of some assistance to 

 zoologists if a naturalist endowed with the skill and 

 patience of the late Mr. Cash would give us a census 

 of the Difflugia varieties or forms that are found in 

 a particular pond or Sphagnum bog once for every 

 month during a year or two. Such a census might, 

 at any rate, suggest certain coincidences of occurrence 

 which would be worthy of further investigation. 



A few figures are given of two individuals " in con- 

 jugation " {e.g. Difflugia ohlonga, p. 13, Crypto- 

 diffiugia oviformis, p. 79, Nebela collaris, p. 96), but 

 the recent researches of protozoologists render it 

 extremely improbable that a true process of conjuga- 

 tion occurs at all under such conditions as the figures 

 indicate. It may be plastogamy or it may be a late 

 stage of fission that has been observed, the absence! 

 of any indication of the nuclear structures in the! 

 figures rendering it impossible to form an opinion orj 

 this point, but there is really no reason to suppose; 

 that it is conjugation. 



