Mil PREFACE. 



Iii the Onychophora, Willey's paper on Peripatus novae - 

 hritanniae is of great importance, especially in connection 

 with the invagination germ -band in the Insecta and the 

 interpretation of the embryonic membranes. 



Among the numerous additions to the literature on the In- 

 secta, Heymon's works, especially that on Lepisma, are worthy 

 of careful study. Unfortunately, the interpretation of the 

 ontogenetic processes in the Insecta is very difficult, and 

 in consequence we still find a terrible confusion enshrouding 

 the origin of some organs, especially that of the alimentary 

 canal, which a number of recent authors maintain to be 

 entirely ectodermal, a condition which, judging from what 

 occurs in other Arthropods, seems extremely improbable. 



The germ-cells, as in the two previous volumes, are still 

 treated of as mesodermal, whereas, as has been pointed out 

 in the editorial notes to Vols. i. and ii., these cells are probably 

 handed down from parent to offspring as distinct and con- 

 tinuous structures, their identity being temporarily merged 

 in the egg. 



In the present volume I have added more notes and 

 literature and made more alterations in the text than in 

 Vol. ii., and I hope that such alterations will tend to bring 

 this volume more up to date. 



MAETIN F. WOODWARD. 



Royal College of Science, London. 

 July, 1899. 



