INVEKTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 761 



tlie many groups taken as examples, then the Darwinian theory must 

 be demonstrable, if at all, from the evidence thus afforded. 



Direct contradiction is also given to the evolutionist doctrines by 

 the fact of the periodicity of the development of animal life which 

 is seen to have been the rule in past times : i. e. epochs of active deve- 

 lopment were succeeded by times of comparative rest, and the develop- 

 ment itself varied in intensity. It is contrary to the analogies afforded 

 by the j)resent order of things to suppose this to be due to changes in 

 the external conditions, for these may cause redistribution but not 

 transmutation of plants and animals. Again, the relation of the 

 faunae and floras of consecutive geological periods to each other shows 

 a co-ordination closely resembling that of those of neighbouring dis- 

 tricts at the present time, in having a number of species in common, 

 a nimiber of decidedly different ones, and a small number of forms 

 differing scarcely more than as varieties from some belonging to both 

 districts. 



If this relation is sought to be explained by the missing species 

 yet to be discovered, it may be replied that if investigation succeeds 

 in finding in one formation the (e. g.) 50 representative species neces- 

 sary to show its absolute sequence upon the preceding formation, it is 

 as likely also to find (e. g.) 500 more species in that formation, and 

 thus set theorists again to work to find these species also in the beds 

 following. The asserted completion of the organic series by fossil 

 links is unfounded, for though, as in the Ungulata, many gaps are 

 thus filled up (by Anchitherium, &c.), yet as many more are created 

 by the discovery of wholly new types (as Brontotherium, &c.) ; so 

 with the mesozoic reptiles and fish and Cephalopoda, and still more 

 with the palaeozoic fauna ; in particular, Professor Claus's declaration 

 (in a lecture at Vienna in 1876) of the surprisingly small help 

 which he has derived from the fossil forms in making out the genea- 

 logy of the Crustacea, is brouglit forward in support. The number 

 of its zones of life must be taken into account in reckoning the 

 changes undergone by organisms in any geological period ; for 

 instance, 153 zones are distinguished from the Silurian to the present 

 age, and 33 in the Jurassic rocks, the passage from each zone giving 

 the necessary conditions for mutation of a species ; but taking the 

 actual number of such changes observed in the case of the Cephalo- 

 poda (a highly modifiable group), in passing through the Jurassic 

 rocks, viz. 77, the conclusion is drawn that on an average only 

 24 periods of change can actually have occurred for any group of 

 animals since the Silurian times, a number quite insufficient to 

 account for the immcuso (asserted) development of new genera, 

 families, orders, and classes since that time. 



B. INVERTEBRATA. 



Mollusca. 

 Mollusca of the 'Challenger' Expedition.*— The Rev. R. B. 

 Watson gives the following as a few points which stand out with 

 Bpecial prominonco as the result of his study of this material 

 * ' Jouiu. Liuii. Soc' (Zool.), xv. (1880), p. 87. 



