116 Annals Entomological Society of America [Vol. XI, 



In the above-mentioned resume of 1899 Heymons takes up, 

 point by point, Verhoeff's work on Coleoptera and Hemiptera, as 

 well as his papers on Tracheates and Myriapods in general, all 

 published between 1892 and 1898. From the results of his 

 review of these investigations Heymons concludes that there is 

 little support for Verhoeff's opinions. The latter include the 

 homology of the styles which are attached to the coxee of the 

 mesothoracic and metathoracic legs of Machilis, as well as to 

 certain abdominal somites of other Thysanura. According to 

 Heymons, Verhoeff compares the style-bearing sclerites, which 

 he considers laterad of, and fused with, the true abdominal 

 sternites, with flattened out coxae, and that rightly, according 

 to Heymons; but, going further caudad, Verhoeff also homol- 

 ogizes the median genital appendages with the distal segments 

 of the legs, and the lateral gonapophyses with the coxae of these 

 legs, therefore regarding the origin of two pairs of genitalia 

 from one pair of ambulatory appendages belonging to one 

 somite, instead of from two pairs belonging to two successive 

 somites, or, to put it from He'ymon's point of view, from at 

 least four isolated evaginations having no connection with the 

 anlages of the segmental appendages found in the embryo. 



One objection which may be made to Heymons's theory, on 

 general morphological grounds, is found in certain of his con- 

 clusions which he himself states as follows: "Heymons zufolge, 

 sind die Geschlechtsanhange mannlicher und weiblicher Insekten 

 nur als Hypodermisfortsatze zu betrachten," and "Die Ge- 

 schlechtsanhange sind, nach der Ansicht von Haase, Peytoreau, 

 Heymons, u. a. erst innerhalb der Klasse der Insekten 

 erworben." With but few exceptions we find that, in tracing 

 the morphological history of almost any organs we may mention, 

 more or less important and well developed in a group of animals, 

 they have not recently "sprung into being" as it were. Nature 

 is not in the habit, to put it differently, and perhaps in a trite, 

 old-fashioned manner, of building structures out of "etwas 

 Neues." A glance at the history of almost any vertebrate 

 structure will reveal an example of this fundamental principle. 



Wheeler realized the necessity of tracing organs not only in 

 the embryonic stages, but also on through later ones. In his 

 paper on Xiphidium he says that the embryonic history of the 

 gonapophyses could be "continuously traced," since there is no 

 flexure of the abdomen in that embryo as exists in so many other 



