6o6 



NATURE 



[April 30, 1903 



closer con mction of these two groups (p. 25). Thus 

 we are told categorically that we need not look any 

 further in this direction for the vertebrate ancestors. 

 But in spite of this, on p. 338, the epithelial lining 

 of the bloodvessels is spoken of " als ein erst den 

 Tunicaten und von da den Vertebraten gewordener 

 Erwerb." The remark on p. 25— that the origin of 

 the Vertebrata is not quite strange to the Invertebrata, 

 since the organisation of the former exhibits nothing 

 absolutely new, nothing which does not crop up in 

 some one of the other phyla— sounds rather flat, and 

 conveys little comfort to him who is anxious to learn 

 what the greatest authority has to say about their 

 descent. 



I. ungs and Air-bladders, p. 256.— Certain Sela- 

 chians possess a dorsal blindsac opening into the 

 oesophagus, perhaps the forerunner of the airbladder 

 of other fishes. Since this diverticulum exists in 

 Selachians only during their early life and vanishes in 

 the adult, 



" \\ ird es als rudimentaeres Organ zu deuten sein, 

 wobei nur fraglich bleibt, wie der ausgebildete Zustand 

 sich verhielt, und ob es je einen solchen besessen hat." 



Are here not mixed up 'the two opposites rudimentary 

 and vestigial? If this organ never was in a complete, 

 functional condition, it would be a rudiment in the sense 

 of incipient evolution. But our author can only mean 

 vestige or remnant. 



Concerning the question of the homology of air- 

 bladders and lungs, a view still frequently advocated, 

 we are told clearly, on p. 216, that 

 " from the low stage of the future lungs are derived 

 other organs which do not yet have a respiratory 

 function, namely, the so-called airbladders of the 

 fishes. Consequently we do not meet with the lungs 

 as such from their first beginning, but as air-receiving 

 organs of other significance. Only gradually they 

 become capable of competing with the primary 

 respiratorv organs (the gills) and are thereby turned 

 into lungs." 



But on p. 256 we are informed, upon the ground 

 of want of proofs of the change of airbladders into 

 lungs, that more likely the airbladders and lungs are 

 akin to each other only in so far as both are evagina- 

 tions of the £ut, but that both have started very early 

 upon opposite roads. In other words, the text is 

 flatly contradicted by the small-printed later addition. 



Gills. — On p. 239, the inner gills of the Anura 

 are properly derived from their outer gills, a modifica- 

 tion which has been studied by Maurer and others. 

 On the next page, however, the outer gills of the 

 Anura are derived, a la Boas, from the true inner 

 gills of fishes, and on p. 341 we are told that the 

 former, first, derivation means a gap in comparison 

 with fishes. Of course there would be a gap, since 

 the two statements, the first correct, the second a 

 baseless assumption, are absolutely contradictory. 

 This muddle could not have happened unless the small 

 tvpe of pp. 240-241 was a later addition to the text. 

 Vascular System, pp. 337-339. — The participation 

 of the endoderm in the formation of the heart of 

 Amphioxus is certain. Very valuable is the fact that 

 the endoderm contributes to the vascular system, 

 NO. 1748, VOL. 67] 



heart and vessels of certain Elasmobranchs, but it is 

 gradually superseded by the mesoderm. It is doubt- 

 ful whether the case of entirely mesodermal formation 

 is a reversion to the original condition. Since the 

 endodermal origin stands in opposition to whal 

 happens in almost all the bilateral invertebrates, we 

 conclude that the change took place already in the 

 Tunicata, viz. that endodermal growth has been 

 acquired by them, whence the Vertebrata have taken 

 it over. Now, having had to conclude that the en- 

 dodermal origin of the vascular system of Tunicata and 

 Vertebrata is a secondary feature, which is still pre- 

 served in but a few cases, the question arises whether 

 the mesodermal origin is to be explained by a reversion 

 to the original condition or whether it is (p. 339) once 

 more (wiederum) a csenogenetic feature. We desist 

 from answering these questions, 



" da in den Thatsachen nichts geaendert wird, und 

 durch Caenogenese auch etwas Altes entstehen kann, 

 nach den Beziehungen die alt und neu besitzen." 



He who understands the above sentence, to the exclu- 

 sion of doubt, will be able to translate it. 



Could the author not apply to the solution of the 

 discrepancy the same principle of the suggestion which 

 he makes on p. 416, apropos of 



" the origin of the lymph-follicles reveals the lymph- 

 cells as derivations of the endoderm. The primitive 

 condition is lost in the Placentalia, not because the 

 endoderm has handed over its function to other 

 tissues, but because the latter have received their en- 

 dodermal share at a much earlier ontogenetic 

 period "? 



Heart, p. 345. — The heart of reptiles, birds and 

 mammals passes temporarily through the stage of a 

 double tube. On p. 345 this is explained as an un- 

 doubtedly secondary feature, due to a special adapta- 

 tion to nutritive arrangements, nameiy, the accumula- 

 tion of fopdvolk, on or in the wall of the gut. In 

 the Mammalia the double anlage still occurs, in spile ol 

 the loss of the yolk. This is certainlv an ingenious 

 and possibly correct explanation, but the reader will 

 miss an) allusion to Elasmobranchs, with their un- 

 paired heart-tube and great mass of yolk. He may 

 further wonder from which class of animals the mam- 

 mals have taken over this feature, if, as our author 

 contends repeatedly, the reptiles are to be excluded 

 from the mammalian line of descent. 



( 'oei inn and Vermiform Appendix. — On p. 171, speak- 

 ing of the end-gut, he emphasises his former sugges- 

 tion that the finger-shaped gland of Selachians is the 

 forerunner of the ccccum ; a complex of glands which 

 pour their secretion by one duct into what marks the 

 upper end of the end-gut. Such glands must neces- 

 sarily have started from the endoderm, but on p. 174 

 we find the following perplexing statement : — 



" The independence of the ccecum is (in [guana) 

 must strongly shown, and thereby we come to that 

 organ which the Selachians possess as the finger- 

 shaped gland, originally foreign to the gut-wall, but 

 raised to permanent value by the connection with 

 the latter." 



As here expressed, this can only mean that once 

 upon a time there existed a fluid-secreting gland, in 



