6 INTRODUCTION 



VII. CRUSTACEAN PARASITES. CRUSTACEA (part of). A large 

 number of species belonging to various well-marked sections of 

 this great class of Invertebrates are parasitic in their habits, most 

 of them being comprised in the so-called haustellated group. 

 They are familiarly known to zoologists as Epizoa. As this 

 latter term implies, they are strictly ectozoal in character, 

 most of the species victimising fishes by attaching themselves, 

 not only to the general surface of the body, but also to the 

 eyes, and especially to the gills or branchiae. The species for 

 the most part belong to the families Lernaida, Caligida, Diche- 

 lestidcp, and Argulidce. In this category must likewise be 

 placed two other families belonging to the so-called isopodous 

 section of edriophthalmatous crustaceans. These are the Cymo- 

 thoida, which attach themselves to the tails of fishes, and the 

 Bopyrida, which occupy the branchial cavity of shrimps. The 

 nature of this work precludes any detailed notice of the 

 numerous members of this section. 



VIII. INSECT PARASITES. INSECTA (part of). The insects, 

 properly so called (that is to say, arthropodous, evertebrated 

 creatures, with six legs), are many of them essentially parasitic 

 in their habits. The most important of these are " bots " 

 and other larvae or maggots of various flies (Diptera). 

 The varieties of lice are also included in this group. Some 

 few of the insect parasites are strictly entozoal in habit, at 

 least for a part of their lifetime, being previously attached 

 externally for a short period only. Most of the forms are 

 essentially ectozoal. A very large number of insect tormentors, 

 although deriving nourishment from their victims, attach them- 

 selves to the animals for so short a time that they cannot be 

 classed as parasites under the ordinary acceptation of the term. 

 As examples of the so-called free parasitism, the autumnal 

 flies (Tabanid&!) and Stomoxys may be cited. Although embrac- 

 ing but few strictly parasitic forms we have the following : 

 (Estridce, Eippoboscidce (with Melophagus), and Nyctcribiida. 

 In regard to the maggots of Muscida and Sarcophaga, some of 

 them are parasitic on animals and man, whilst others are 

 parasitic upon insects themselves. The larvae of Cono>hl<v 

 attack humble-bees internally. Those parasitic insects, pro- 

 perly so called, which, like certain of the crustaceans, are some- 

 times spoken of as epizoa, comprise three well-marked families. 

 Thus, we have Pediculidce (the source of lousiness), Philo- 

 pteridae, and Liotheida. Both of the latter embrace numerous 



