i'HE MALLOl'lIAGA OK IJITINU LICK. .53 



difference between the birds ; the temperature of the host's body, the 

 feathers asfnod, all the conditions of the environment are essentially un- 

 changed in their relation to the parasite." The parasitic species may 

 thus remain unchanged, whilst the bird species may have become 

 differentiated into a dozen specific forms, all with a common parasite. 

 The possibility of this explanation being true is largely increased by 

 the fact that there is no known case Avhere the same species of parasite 

 affects Old World and New World species of birds, which are widely 

 separated phyletically. 



The peculiar conditions relating to those species of Mallophaga that 

 live on hosts of non-gregarious habits niust also be considered. It is 

 possible that in birds of monogamous habits the parasite becomes almost 

 entirely cut oft' from its own kind, and, for many years, in-and-in 

 breeding alone takes place, the only possible chance of a cross being 

 when a fresh selection of a mate occurs. This isolation will soon 

 mark the race, and the conditions will prevent the production of any 

 wide divergence in the same species. It will create a great number of 

 small variations in the same species, but, at the same time, it Avill tend 

 to preserve practically unchanged (except for these trivial specific 

 variations) the specific homogeneity of the parasites, and hence Kellogg 

 says that, whilst he can refer a score of species taken from American 

 birds to species described from p]uropean or Asiatic birds, yet, in all 

 these cases, there are slight but recognisable differences between the 

 Old World and New World specimens. 



Some birds have as many as six species of Mallophaga parasitic 

 on them, others have tw^o or three, whilst in others a parasite is con- 

 fined to a single species or genus. It happens very rarely, however, when 

 more than one species of parasite is found on a bird, that the parasites 

 belong to the same genus. Usually the parasites belong to widely 

 different genera. 



The position of the Mallophaga among insects is still open to 

 question. They have been included in Hemiptera, because the 

 rrdindidac (or sucking lice) belonged there, and both are external 

 parasitic insects on mammals and birds. Then they were removed to 

 the Platyptera in the neighbourhood of Termites, Psocids, Perlids 

 and Enibids (and are even retained there now by Dr. Sharp), and 

 more recently, i.e., since the Platyptera were broken up by Brauer, 

 Mallophaga have been created into a separate Order. Their 

 specialisation — in the hne of degradation — is such that it is difficult 

 to relate them closely with any other insects. 



For British students, we do not know whether any work later 

 than Henry Denny's Monnf/rcqthia Annplnrovuni hrittaniae or An 

 T-r.s.srt// 11)1 the British Species of Parcmtic Insects, 1842, London, illus- 

 trated with coloured plates, has been published. Some good general 

 remarks on the Order are to be found in the The (_'ainbri<l(/e Xatiiral 

 llistnn/, vol. v., by Dr. Sharp, but he states that the development of the 

 Mallophaga " is very imperfectly known,'" so that a specialist at the 

 Order is sure to break virgin soil. Dr. Sharp gives no generic or 

 specific characteristics, and hence his chapter is of no use to the pure 

 systematist. 



We have been tempted to write th(^ above : (1). Because an up-to- 

 date monograph of the British (and European) ^[afj^ophaga, with 

 notes on habits, life-histories, etc., is very badly needed. (2). Because 

 we have received for review a valuable work on the Order, by Mr, 



