AMERICAN ZOOLOGISTS AXD EVOLUTION. 109 



uses the 'theory of descent' as a -working hypothesis, without which 

 no one studying any group of animals in the period of its rise and 

 most rapid evolution can expect to do otherwise than stumble and 

 wander astray. To refuse it is to merit failure." 



Professor J, S. Kingsley, in his study of Limulus, regards it as an 

 Arachnid, but states that its ancestors take us back to a time when 

 the distinctions between the Crustacea and Arachuida were far less 

 marked than now. 



Dr. A. S. Packard,* in a paper on the " Genealogy of the Insects," 

 shows by means of a " genealogical tree " the descent of the class 

 from the Thysanura, with some hypothetical creature not unlike Sco- 

 lopendrella, as the probable stem-form of the hexapods. It is through 

 the resemblance the larviB of the different orders of insects bear to 

 various members of the Thysanura that this scheme is justified. It 

 may not be out of place to say here that the use of the " genealogical 

 tree," in suggesting the probable line of descent of various allied 

 groups, has been severely condemned by some as leading to no practi- 

 cal good in classification. It seems to me, however, the only clear 

 scheme for the proper working out of the ascertained or hypothetical 

 relationships of animals ; it is thought-exciting, its very attitude pro- 

 vokes studious inquiry and suggestive inferences. It may be called 

 the modern tree of knowledge. 



The modern genealogical tree as used by the biological student 

 (and as well by the ethnologist, philologist, and others) is a graphic 

 diagram of the relationships between groups as understood by the pro- 

 jector, and, as such, is a most commendable and useful method with 

 which to illustrate his meaning. With additional knowledge one can 

 see at a glance the points that need strengthening, and he can pare, 

 prune, or even graft new fruits on the old stock, or, if it is rotten at 

 the trunk, cut it down altogether. These trees have always been in 

 vogue with the older naturalists, only, in the old style of arboricultiire, 

 the trunk was always kept stiffly vertical, while the branches were 

 bent down and tramed horizontally, being flirasily attached to the 

 main stem by printers' devices of long and short brackets. In this 

 attitude it reminded one of the dwarfed and deformed trees of the 

 Chinese, and very properly typified the dwarfed and deformed way of 

 looking at classification. 



Never was the provisional use of a genealogical tree more com- 

 pletely justified than in a memoir by Dr. Alexander Agassiz f on the 

 " Connection between Cretaceous and Echinid Faunge." He certainly 

 speaks in no uncertain terms when, in considering the Spatangoids of 

 the chalk, he says, " They lead us directly through the PalmoatomincB 

 and the Collyritidm to the Anancliytidm which have persisted to the 

 present day," and other relationships of the same nature are repeated- 



* " American Naturalist," vol. xvii, p. 932. 



f " American Journal of Science and Arts," vol. xxiii, p. 40. 



