PREFACE vii 



combination drawings or modified in one respect or another in 

 accordance with my own ideas and dissections. 



A few words of explanation are necessary in regard to the 

 choice of material. I tried to use only American species but 

 this proved difficult in the case of Trematodes and leeches. I 

 have examined many species of Trematodes but none of them 

 is comparable to the common, small, European liver fluke, 

 Dicroccelium lanceatum. This species does not occur in the 

 Western Hemisphere, but it is a truly typical representative of 

 its class and so common in Europe that it may be bought of 

 foreign firms in unlimited quantities. The medicinal leech is 

 for sale alive in this country and there is therefore no special 

 advantage in giving preference to indigenous species which one 

 would have to collect since they are not on the market. I tried 

 also to avoid species which are usually studied in the Freshman 

 year in the course in General Biology. Experience has shown 

 me that the students resent repetition and surely there is no 

 need for it. As long as the student is required to take General 

 Biology or Elementary Zoology preparatory to Invertebrate 

 Zoology, a diversity of material is of distinct advantage. An 

 unfortunate exception had to be made in the case of the Earth- 

 worm, but I do not know of any convenient substitute. A con- 

 cession to tradition had to be made in the case of the locust. In 

 my opinion a roach is to be preferred, because it is easier to 

 dissect and because it may be kept alive in winter; but private 

 conversation with various colleagues has convinced me that it 

 would not do to leave out the grasshopper. Some groups had 

 to be omitted altogether on account of lack of space. If the 

 book meets with favorable reception, new chapters may be 

 added in a later edition. 



The detailed descriptions in the manual of the anatomy of 

 animals which the student is given to dissect, will relieve the 

 teacher of the necessity of lecturing on this subject. His time 

 may be better spent in giving a general account of the group 

 to which each animal belongs and in treating broader aspects 



