956 WOKMS 



the anterior. 1 In the Leech tribe the dental apparatus with which 

 the mouth is furnished is one of the most curious among their 

 points of minute structure, and the common ' medicinal ' leech 

 affords one of the most interesting examples of it. What is 

 commonly termed the ' bite ' of the leech is really a saw-cut, or 

 rather a combination of three saw-cuts, radiating from a common 

 centre. If the mouth of the leech be examined with a hand- 

 magnifier, or even with the naked eye, it will be seen to be a 

 triangular aperture in the midst of a sucking disc, and on turning 

 back the lips of that aperture three little white ridges are brought 

 into view. Each of these is the convex edge of a horny semicircle, 

 strengthened by a deposit of carbonate of lime which is bordered by 

 a row of eighty or ninety minute hard and sharp teeth ; whilst 

 the straight border of the semicircle is imbedded in the muscular 

 substance of the disc, by the action of which it is made to move 

 backwards and forwards in a saw-like manner, so that the teeth are 

 enabled to cut into the skin to which the suctorial disc has affixed 

 itself. 2 



1 See Professor A. G. Bourne, 'On Budding in the Oligocheeta,' Report Brit. 

 Assoc. 1885, p. 1096. 



2 Among the various sources of information as to the anatomy and physiology of 

 the Annelids the following may be specially mentioned : the ' Histoire Naturelle des 

 Anneles Marins et d'Eau douce ' of M. de Quatrefages, forming part of the Suites a 

 Buffon ; the successive admirable monographs of the late Professor Ed. Claparede, 

 Recherches Anatotniqu.es sur les Annelides, Turbellaries, Opalines et Gregarines, 

 observes dans les Hebrides, Geneva, 1861 ; Recherches Anatomiques sur les Oligo- 

 chetes, Geneva, 1862 ; Beobachtungen iiber Anatomie und Entwickelungsgeschichte 

 wirbelloser Thiere an der Kilste von Normandie, Leipzig, 1863 ; and Les Annelides 

 Chetopodes du Golfe de Naples, Geneva, 1868-70 ; the monograph of Dr.Ehlers, Die 

 Borsienwiirmer (Annelida Chcetopoda),^ 1864-68. With the exception of Professor 

 Mclntosh's article in the Encyclopedia Britannica, and the various articles on 

 ' Worms ' in the Cambridge Natural History, which can be warmly commended to 

 the student, most of the recent papers on Annelids have dealt with small groups only, 

 but of these a very large number has appeared. For the descriptions of new forms 

 the memoirs of Grube, Mclntosh, and St. Joseph are especially to be consulted; 

 Hatschek, Kleinenberg, and Salensky have written the most important contributions 

 to our knowledge of development ; Benham, Bergh, Bourne, Eisig, Meyer, Perrier, 

 and Whitman have, among others, added to our knowledge of their anatomy and 

 morphology. 



