324 



among the former, as it is difficult to see what modifications, other 

 than being absolutely poisonous perhaps, could protect the smaller 

 against the larger creatures in such circumstances. 



In the chapter on the fresh-water Crustacea the ver}'' puzzling 

 but nevertheless very interesting problems of distribution come 

 very? much to the front. It is shown that, generally speaking, 

 fresh-water Crustacea, in common with most other fresh-water 

 organisms, have a remarkably wide distribution, some species even 

 being cosmopolitan. On the other hand, some individual lakes 

 such as Tanganyika and the Caspian have developed quite peculiar 

 faunas of their own. The wide range of some species is probably 

 easily accounted for by the fact that they produce special eggs, 

 e.g. the " ephippial " eggs of the Cladocera, which can be dried 

 and blown or carried about without injury. But other widely 

 distributed species do not produce such eggs, and it may be that 

 in these cases the adults themselves can survive long journeys. 

 The recently discovered fact that certain species of Cycloj^s and 

 Canihocam'ptus have the habit of surrounding themselves with a 

 cocoon-like capsule of mud particles seems to throw a new light 

 on the possibilities in this dii^ection. 



The two chapters specially mentioned above contain the bulk 

 of the references to micro- Crustacea to be found in the book, but 

 naturally there is also much of interest on the smaller forms in 

 the section dealing with the Crustacea as parasites. Of these 

 perhaps the most curious case alluded to is that of the Monstril- 

 lidse, in which the animals are hatched as free-swimming nauplii, 

 then become so absolutely parasitic within the body of a marine 

 worm that each consists only of a little ovoid mass of cells, which, 

 however, finally develops into a free-swimming adult, but minus 

 all trace of appendages between the antennae and the first pair 

 of feet ! 



Dr. Caiman is to be ^congratulated on the appearance of this 

 compact, up-to-date and beautifully illustrated "- Life," and it is 

 sincerely to be hoped that the book will find a wide circle of readers 

 and do much to stir up further interest in a group of animals 

 which has not yet received the amount of attention it deserves. 

 In view of probable future editions two little suggestions may be 

 permitted perhaps. A word so long and so widely used as 

 " Entomostraca " should surely be mentioned somewhere, if only 

 in a footnote, and such phrases as " slightly enlarged," '* much 



