565.3 -397 



IV 



Fossil Apodidae 



EVERY group of animals contains in itself its own record if we 

 could but decipher it. The zoology of the future is bound 

 under the fascination of this idea to devote itself to an ever closer 

 comparative study for the express purpose of gaining insight into 

 the lines of their past development. "We have no royal roads, and 

 the hopes which were held out to us a few years back that embryology 

 would provide us with one have not been realised. It can only 

 supply us with hints, the full meaning of which we must learn by 

 other methods. Most hopeful of good result are those groups in 

 which allied forms, recent and extinct, offer themselves in sufficient 

 numbers for comparison. None can compare in this respect with 

 the Crustacea. There is an enormous wealth of known crustacean 

 forms extending upwards from the very lowest fossiliferous strata 

 and still swarming in every suitable part of the globe. The 

 problem has long been to find a genealogical key to reduce this 

 immense stream of organised life to some order of development. 



The first and most striking feature noted was the fact that all 

 but the most extreme forms are segmented, and the natural inference 

 was that the common ancestor of the whole immense family must 

 have been some less specialised segmented form. Of recent years 

 the attention of zoologists in search of the most primitive form 

 among existing Crustacea has been concentrated upon the freshwater 

 Apus which appears sporadically in rain pools all over the world. 

 "When the pools dry up the eggs remain in the mud ; indeed it is said to 

 be a necessary condition of development that they should be so dried. 

 How long they remain capable of development is not known. These 

 facts are interesting because they suggest to us a way in which Apus 

 may have survived, practically isolated from the struggle for exist- 

 ence, almost unchanged from the days when the Crustacea first 

 appeared on the planet. Those who claimed the primitive character 

 of Apus were not disconcerted by the absence of fossil remains which 

 could be definitely assigned to Apus. There was, of course, always 

 the hope that such might be found, and further there was the strik- 

 ing fact to which they could appeal that one of the most prolific of 

 early crustacean forms, the Trilobites, possessed many characters in 

 common with Apus. The great Paleozoic family of the Trilobites 



