128 BKIT1SH TYKOGLYPHIM!. 



case of exceptional genera such as those above men- 

 tioned), and prior to the last ecdysis ; in giving this 

 definition, however, it may be necessary to except the 

 case of the Analgesinae (a large group of Sarcoptidse 

 which are found on the feathers of birds, and are 

 called by Robin and Megnin " Sarcoptides plumicoles ") ; 

 the female in many species of this sub-family, and 

 probably in all, does change its skin once after coition 

 with the adult male, and after this final ecdysis the 

 female is in many species extremely different in appear- 

 ance from what it is before it. Megnin apparently 

 regards this as a case in which there are two successive 

 forms of adult female, viz. the nubile female and the 

 reproductive female ; but it will probably be considered 

 that it is rather to be looked upon as a case of pedo- 

 genesis. It would be extremely interesting to trace 

 the life-history of one of these species, and ascertain 

 for certain whether the female passes through the 

 same number of ecdyses as the male or more, which 

 would afford a substantial indication as to whether the 

 nubile female is a nymph or an adult ; but minute 

 creatures like the AnalgesinaB, which are parasitic 

 upon such things as birds, and will not live away 

 from the host, and are usually present in numbers if 

 at all, are anything but easy to watch the life-histories 

 of in such a manner as to be reliable upon such points 

 as the number of ecdyses ; to ascertain which a single 

 specimen must be observed throughout the period 

 between its emerging from the egg and its becoming 

 an imago. 



Megnin' s definition of the expression nymph was the 

 creature after it had become octopod, and before it 

 had any external sexual organs ; further investiga- 

 tions, however, have shown that this cannot be main- 

 tained, because in a great proportion of the Acarina 

 the nymph in the stage between the penultimate 

 change of skin and that which brings it to the adult 

 condition does possess external sexual organs, although 

 they may be of small size, and, with the exception 



