DEVELOPMENT AND IMMATURE STAGES. 127 



In a former work * I have explained the sense in 

 which I use the expressions "larva" and "nymph," 

 as applied to the Acarina ; but it may be convenient 

 to repeat it here, because the other volume is not 

 always at hand, and authors have not by any means 

 been agreed as to the meaning of the terms in this 

 connection. 



The expression larva is used in this book to signify 

 the creature after it has emerged from the egg, and 

 while it is still hexapod, or has a smaller number of 

 legs than six ; as occurs in Phytoptus, where even the 

 adult only has two pairs of legs, the others being 

 abortive ; or while it is without legs, as occurs in the 

 larvae of some Demodicidae, w^here the legs are some- 

 times entirely absent in this stage and sometimes 

 represented by three pairs of small tubercles which 

 can hardly be termed legs. It has been stated that 

 the larvae of Pteroptus are octopod at birth ; the 

 assertion, however, requires confirmation. Even if it 

 be true that when Pteroptus leaves the egg it has 

 already acquired its full number of legs, it would 

 doubtless mean only that the larval stage, such as it 

 is now usually recognised to be in Acari, is suppressed 

 or passed within the egg. What is here called the 

 " larva " Nicolet called the " young larva," reserving 

 the term " larva " without the adjective for what in 

 accordance with the present practice of acarologists I 

 call the " nymph." Henkin, and one or two others 

 following him, call the larva while still within the egg- 

 membrane the " Schadonophan ; " this was with refer- 

 ence to Trombidium, the egg of which has a dentoval 

 stage, t 



The expression " nymph " is used in this book to 

 signify the creature after it has become octopod (or 

 has attained its full ultimate number of legs in the 



* ' British Oribatidse,' London (Ray Society), 1884, p. 66. 



f " Beih-a^e zur Anatomie, Entwicklungsgeschichte mid Biologie 

 von Trombidium fuliginosum" in ' Zeit. wiss. Zool.,' Bd. xxxvii (1883), 

 p. 596. 



