^0 K. KISHIXOUYË. 



■ 



lîimellaî becomes the operculum of the kmg-book after it is depressed 

 in height. Judging from figures (figs. LXXIX and LXXIX') 

 given in " On Insects and Arachnids," Bruce seems to have mistaken 

 the caudal prominence of the early period of this stage (see my figs. 

 24-28) as the operculum of the lung-book. According to him tlie 

 abdominal nppendage is invaginated to form the lung-book, but as 

 we have seen, it is not so. Locy has correctly described the forma- 

 tion of the lung-book lamella3. He says that the lungs arise from 

 infoldings ; but he is silent about the place where these infoldings 

 arise. 



In the basal |)art of the second abdominal a[)[)endage on the 

 interior side, another ectodermic invagination is produced. It as- 

 sumes the shape of a deeply invaginated tube and remains in this 

 condition till after the time of hatching. The appendage itself is not 

 invaginated and becomes from this time gradually shorter. 



It is very probable that the lung-books were derived from the 

 gills of some aquatic arthropodous animals such as Limulus ; for 

 the lunof-books are nothinsf more than the lamellar branchia3 of 



O a 



Limulus sunk beneath the body surface. The tubular trachea may 

 afterwards have been derived from the lunsr-books. The branchin 1 

 lamella} of Limulus are formed as outgrowths <jf the ectoderm at the 

 lower (posterior) surface of abdominal appendages, and those of spiders 

 are also produced really in the lower surface of the fii'st abdominal 

 appendage (in the dipneumonous spider). Hence I tliink that the 

 spider with two pairs of lung-books is the most primitive one, and 

 the one with one pair of lung-books and the other pair transformed 

 into the tubular tracheai is more primitive than the spider with only 

 one pair of lung-books. I cannot agree with the view of some 

 authors who maintain that the luno'-book is derived from a chister ol 

 tracheœ. 



