PREFACE. 



The present and third instalment of the translation of the 

 Lchrhuch der vergleicheoiden SntwicMungsgeschicMe der wirhel- 

 losen Thieve contains the Arachnida and appended groups, the 

 Onychophora, the Myriopoda, and the Insecta, thus completing 

 the Arthropodan portion of this work. The remaining volume, 

 which contains the Mollusca, Ascidia, and Cephalochorda, will, 

 1 hope, be published at the end of the year. 



In connection with the present volume, I have to thank 

 Mr. B. I. Pocock for his valuable assistance in the Arachnidan 

 part, and also I have to thank Mr. A. D. Michael, who kindly 

 read through the chapter on the Acarini and corrected many 

 errors in the same. Most of the suggestions made by these 

 gentlemen have been added as editorial footnotes, but some 

 matter, when the original was obviously at fault, has been 

 placed in the text. 



The very important work by Brauer on the Ontogeny of 

 the Scorpion renders some of the text relating to this genus 

 out of date, and this work should certainly be consulted by 

 those studying the Arachnida. His discovery of an additional 

 segment between the thorax and abdomen is of especial 

 importance in the interpretation of the Arachnidan body. 

 In this connection it is interesting to note that this segment 

 was correctly figured, though misinterpreted, by Metschnikoff 

 in 1871, as a careful comparison of the figures of these two 

 authors will show. 



