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SCIENCE 



[N. S. Vol. XXXVII. No. 956 



eurypterids, but that all three, while related, 

 have early separated, and that eurypterids are 

 still nearest in their general aspect to this 

 common ancestor"; and (3), while we have 

 no clue as to what this common ancestor was, 

 it is clear that the earliest and most primitive 

 known Crustacea (trilobites) do not stand in 

 that relation, and therefore the derivation of 

 various types of these arachnids from arthro- 

 pods more primitive than the crustaceans 

 seems a necessary inference. It is recalled in 

 this connection that Bernard derives the 

 Crustacea from a bent carnivorous annelid, 

 and that Beecher regards this view as partly 

 confirmed by his discoveries concerning the 

 yentral anatomy of trilobites. 



For the study of the ontogeny of eurypterids 

 (the authors had at their command an un- 

 rrivaled series of larval stages of four genera, 

 ■ranging in size from a length of 2 mm. or less 

 «p to the adult condition. A comparison of 

 igrowth stages leads to the important conclu- 

 sion that there is a " general parallelism in 

 the ontogeny of the eurypterids and Limu- 

 lus." Not less brilliant and far-reaching is 

 the discovery that the Cambrian genus 8tra- 

 hops fulfills tolerably well our conception of a 

 generalized prototype from which Silurian 

 eurypterids have descended. The adult Stra- 

 bops so closely resembles the young of later 

 genera as to justify the statement that euryp- 

 terids actually pass through a " Strabops 

 stage " during their nepionic development. 

 ■Herein is found fresh evidence in favor of the 

 Bo-called recapitulation theory, or biogenetic 

 law, as important in its way as the recogni- 

 tion of the " Prestwichia stage " of Limulus, 

 and the goniatitic and ceratitic stages of am- 

 monites. 



Confirmatory evidence in favor of the ho- 

 mologies between eurypterids and king crabs 

 is found in the fact that Pterygotus and Limu- 

 Itis show a remarkable identity in structure of 

 the compoimd eyes. The view of their com- 

 mon relationships thus receives strong sup- 

 port from a new body of facts, for, as shown 

 by Watase and others, the visual organs of 

 'Limulus form an extremely peculiar struc- 

 ttural type. Among the various special anat- 



omies that have been minutely investigated, 

 those which have to do with the compound 

 eyes and genital appendages are particularly 

 commendable, and the results gained are of 

 signal importance. 



The special essay on morphology and anat- 

 omy, together with the discussion as to the 

 mode of life of these creatures, are replete 

 with new and interesting details. Owing to 

 limitations of space, we can only refer to these 

 in the most casual way, and it must suffice to 

 note merely the captions of some of the sub- 

 ordinate themes discussed, as, for instance, the 

 following : Geological distribution and bio- 

 nomic relations; mode of life; taxonomic re- 

 lations; synoptic table of North American 

 eurypterids. These lead up to the principal 

 chapter, consisting of 232 pages, which is de- 

 voted to a systematic account of the group 

 and is in every way most excellent. After this 

 follows an appendix of 40 pages, in which are 

 set forth the results of investigations and dis- 

 coveries made since the body of the work went 

 to press. Besides the valuable note on Si- 

 lurian scorpions, already referred to, there are 

 considered here the relations of several prob- 

 lematical forms, inter alia the pre-Cambrian 

 bodies called Beltina, the genus Hastimima of 

 White, and the suborder Limulava of Wal- 

 cott. Appendices as important as this are 

 welcome in any work for the choice nuggets 

 of new truth they contain. 



The greater part of this memoir necessarily 

 deals with the concrete facts of observation 

 and their adjustment to the present state of 

 our knowledge. Nevertheless, an undercurrent 

 of ideas appears to run through various pas- 

 sages, sometimes only suggested or hinted at, 

 or again included within broad generalizations. 

 And the central thought that informs these 

 ideas proves to be an insistence upon the 

 fundamental human interest of the theme. 

 For really, is not the general theme one which 

 involves questions concerning our own remote 

 ancestry? And who knows whether we may 

 not discover landmarks which shall point for 

 us the way taken by advancing creation in its 

 slow march through the ages, the end whereof 

 is man? A gradual progression leading up to 



