NOTICKS AND REVIKWS. 77 



just taken into the intestine, it is sent out with considerable force, which 

 propels the animal forward with a jerk, several times the length of its 

 own body ; by this means, it keeps out of the way of its enemies." 



In the address of the President (W. Hague Harrington, of Ottawa), 

 mention is made, among many other interesting things, of " Parasitism 

 in Insects." He refers to Professor Riley's work, and divides parasitic 

 forms into three groups : — (I) Pdra'^ites Proper, including insects whose 

 whole life is passed upon, and is dependent upon, their host, and which 

 may be sub-divided into external, as lice, and internal (or sub-cutaneous) 

 as the itch-mite. (2) Fatal Parasites, which, in the larval stage, live 

 at the expense of the members of their own class. These are also 

 sub-divided into internal, where the larva is nourished within the host 

 upon the surrounding fluids, as are the majority of Hymenopterous 

 parasites, and exlp.rnal, where the larva attaches itself to the host (as in 

 Thalessa), and sucks its juices. To this sub-division belong many Hy- 

 menopterous, Diptei'ous and Coleopterous parasites. (3) Inqailiiiom 

 parasites, which include the numerous forms which live upon the 

 provision made by other species, for the sustenance of their offspring, 

 or which are found habitually associated with otlier insects, but not 

 injurious to them. This class is sub-divided into Fatal inqnilines, where 

 the guest's living means starvation and death to the host, and Cominen- 

 sals, where association is mutually harmless, as where beetles are found 

 living in the nests of bees and ants. On the same subject is another 

 article '' The economic value of parasites, and predaceous insects," by 

 Prof. J. B. Smith, but, although interesting enough, the argument 

 throughout is weak, and the logic unsound. The Professor begins with 

 an apparent paradox : " No one can realise more than I do, how much 

 parasites maintain the balance and check the increase of injurious 

 species. I am peifectly aware, that were it not for parasites, many 

 an insect would become so abundant that certain crops could not 

 be satisfactorily grown," and yet he goes on to say: — "In fact I am 

 almost ready to say that parasites have no real economic value to the 

 agriculturist." There is a certain amount of "heroics" about the 

 article that is hardly scientific, and Professor Smith only refers to well- 

 knovvn facts, when he says that " parasites do not exterminate their 

 hosts in any instance ; their mission is merely to interj)ose a check to 

 undue increase." But he goes on to say that the farmer "must depend 

 upon his own exertions to save his crop. There are, however, many 

 insects which are very commonly parasitised, and among them may be 

 mentioned the various species of cut- worms (Noctua larvae). It is 

 nothing uncommon to find in an infested field, that fully one-half, and 

 sometimes as many as three-(piarters of the specimens, will have eggs of 

 the Tachina flies attached to the skin, and probably others have parasites 

 which are not externally visible." Now mark I The writer continues 

 " yet the fact that these cut- worms are infested by parasites, is of 

 absolutely no value to the farmer." And this is the reason for such a 

 conclusion : — " They eat just as much as if they were not parasitised, and 

 it is really a matter of little importance to the agriculturist, wlicther the 

 food that is stolen from him makes a moth or a fly. The caterpillar 

 feeds all the same until it is full-grown. Next year, in the same 

 field, there will be just as many cut- worms as tliere were in the previous 

 year." Just so! "As many," not more. Then this strange logic 

 continues : — " The parasites have kept the number within the same 



