June 17, 1898.] 



SCIENCE. 



835 



He moves somewhat more securely over the 

 ground of histology and embryology, although 

 we find an occasional lapsus or deficiency. As 

 an example of a histological lapsus Professor 

 Packard's account of the origin of the tsenidia 

 of the trachea3 (p. 449) may be mentioned. He 

 describes the spiral thread of the chitinous 

 trachea as originating from nuclei (!) and gives 

 two figures to illustrate this remarkable con- 

 tention. But if these figures show anything they 

 show that the tajnidia arise from the cytoplasm 

 of the tracheal hypodermis and not from nuclei. 



The embryologist may object to Professor 

 Packard's heading a section (p. 126) with the 

 words 'Embryonic development of the wings.' 

 In accepting Weismann's observations, pub- 

 lished in 1864, that the imaginal discs of the 

 legs and wings of the blow-fly are formed before 

 the hatching of the embryo. Professor Packard 

 does not stop to consider that these observa- 

 tions were necessarily unsatisfactory because 

 the method of sectioning the egg was not in 

 vogue at the time. Moreover, an examination 

 of the concluding paragraphs of Graber's study 

 of the embryology of the fly (1889) and of the 

 accompanying figures of sections would have 

 convinced Professor Packard of the uncertainty 

 of the statement that the wing-germs are 

 formed in the embryo, and he would have 

 avoided a misleading heading. Several cases 

 of a similar incautious haste in accepting the 

 statements of authors could be pointed out. 



On the whole the complicated subject of 

 insect morphology is handled with a good 

 sense of proportion. We could have wished 

 for longer chapters and more instructive figures 

 illustrating the fascinating subjects of phospho- 

 rescence, stridulating organs, compound eyes, 

 etc. Stridulatingorgansarenoteven figured. The 

 vast literature on the compound eyes of insects 

 must surely furnish much better figures than 

 those employed by Professor Packard, and a 

 few good sections of one of our common fire- 

 flies would furnish better drawings of the 

 phosphorescent organs than the one taken 

 from Emery's paper. 



In the embryological division of the subject 

 there are many little inaccuracies, as e. g. (p. 

 525) when Professor Packard says: "The 

 germinal vesicle of the ripe insect egg lies in 



the center of the yolk, where it appears as a 

 large vesicle-like cell-nucleus containing a few 

 chromatine elements." If Professor Packard 

 had ever spent hours, days, or even weeks, 

 searching for the germinal vesicle in a ripe in- 

 sect egg, he would not describe it as a ' large 

 vesicle-like ' structure in ' the center of the 

 yolk.' The envelope formation and revolution 

 of the insect egg admits of a more interesting 

 comparative treatment than that employed by 

 Professor Packard. In this connection we ven- 

 ture to say that the inversion of the figures of 

 the (Ecanthus embryo (p. 545), taken from Ayers, 

 will only serve to perpetuate an unfortunate 

 blunder in the orientation of the embryo with 

 respect to the egg. 



It is to be regretted that Professor Packard 

 could not omit all reference to Neo-Lamarckian- 

 ism. In the closing paragraph of the portion 

 on insect metamorphosis we find the following 

 sentence : "The sudden or tachygenic appear- 

 ance of temporary structures, such as hatching 

 spines, various setse, spines, respiratory organs, 

 so characteristic of dipterous larvse and of the 

 protective colors and markings of caterpillars 

 and which are discarded at pupation or im- 

 agination, are evidently due to the action of 

 stimuli from without, to the primary ueola- 

 marokian factors, the characters proper to each 

 larval stadium and to the pupal and imaginal 

 stadia, characters probably acquired during the 

 lifetime of the individual, becoming finally 

 fixed by homochronous heredity." Such lan- 

 guage is out of place in a text-book, unless the 

 other side of the question is also presented. 

 In certain respects insect metamorphosis is one 

 of the least favorable subjects for the study of 

 the 'primary Neo-Lamarckian factors.' The 

 Neo-Lamarckians have yet to demonstrate how, 

 e. g. , many chitinous structures, such as hairs, 

 scales, etc., which are really dead or fixed be- 

 fore they begin to function in the imago, and 

 which have certainly undergone specific or 

 even generic variation since complete meta- 

 phosis was acquired in the common ancestor, 

 can be due to the direct action of external 

 stimuli becoming finally ' fixed by homochron- 

 ous heredity.' 



It would be possible to cite several cases of 

 inaccuracy in Professor Packard's book, were 



