August 26, 1898.] 



SCIENCE. 



257 



same formation. These facts, and the ac- 

 knowledged sudden appearance of large 

 numbers of all the distinct types of inverte- 

 brates in the Paleozoic, and of all the greater 

 number of all existing and fossil types be- 

 fore the expiration of Paleozoic time, speak 

 strongly for the quicker evolution of forms in 

 the Paleozoic, and indicate a general law of 

 evolution. This, we think, can be formu- 

 lated as follows : Types are evolved more 

 quickly and exhibit greater structural differences 

 between genetic groups of the same stock while 

 still near the point of origin than they do subse- 

 quently. The variations or differences may take 

 place quickly in the fundamental structural char- 

 acteristics, and even the embryo may become dif- 

 ferent when in the earliest period, but subse- 

 quently only more superficial structures become 

 subject to great variations.'''^ 



If this applies to the evolution of these 

 cephalopods in the Mesozoic, how much 

 more rapidly and efficaciously did the 

 principle operate in the Precambrian 

 period, after the initial steps in the di- 

 vergence of types from the unicellular Pro- 

 tozoon took place ? The same law or fact 

 obtains with the insects, the eight holome- 

 tabolous orders having, so far as the evi- 

 dence goes, originated at nearly the same 

 geological date, near or soon after the close 

 of the Paleozoic era. Williams also shows, 

 from a study of the variations of Atrypa 

 reticularis, that this species in its specific 

 characters shows a greater degree of vari- 

 ability of plasticity in the earlier than in 

 the later stages of its history. We thus 

 conclude that after the simplest proto- 

 plasmic organisms originated, the greatest 

 difficulties in organic development, i. e., the 

 origination of the founders of the different 

 classes were, so to speak, met and over- 

 come in Precambrian times. The period 

 was one of the rapid evolution of types. 

 As Williamsf has well remarked : 



*Geologioal Biology, p. 322. 

 ■fL. c. p. 347. 



" The chief expansion of any type of 

 organism takes place at a relatively early 

 period in its life history. Since then, as 

 with the evolution of the continent itself, 

 the further progressive differentiation of 

 marine invertebrate forms has, since the 

 close of the Precambrian, been a matter of 

 detail." 



As well stated by Brooks, since the first 

 establishment of the Cambrian bottom 

 fauna, " evolution has resulted in the elabo- 

 ration and divergent specialization of the 

 types of structure which were already estab- 

 lished, rather than in the production of new 

 types." 



In accepting the general truth of this 

 statement, and its application to the marine 

 or Cambrian types it may, however, be mod- 

 ified to some extent. For during the late 

 Paleozoic was witnessed the evolution of the 

 three tracheate, land-inhabiting, air-breath- 

 ing classes of Arachnida, Myriopoda and 

 insects, and of the air-breathing vertebrates, 

 with limbs and lungs, comprising the four 

 classes of amphibians, reptiles, birds and 

 mammals. 



Alpheus S. Packard. 

 (To be concluded). 



BOTANICAL NOTES. 

 ASPARAGUS RUST. 



De. B. D. Halsted, of the New Jersey 

 Experiment Station, has issued a bulletin 

 No. 129) on the Asparagus Eust, its treat- 

 ment and natural enemies, which is of 

 much botanical interest, since it gives good 

 illustrations of all the stages in natural 

 size, and under diiferent magnifications. 

 This rust was described by De Candolle in 

 1805, and given the name which it now 

 bears, Pueeinia asparagi. It has been known 

 in Europe for a long time, but was unknown 

 in the United States before 1896. In that 

 year Dr. Halsted detected it in New Jersey, 

 Delaware, Long Island and some portions of 

 New England. In 1897 and 1898 it has 



