Misce.Ua nenits. 2 1 •'? 



great multitude of small firrnnulcs, wliich take a deep stain from 

 hapmatoxylin, in consequence of which plands and excretory ducts 

 are easily recognizahle in preparations which are treated in this 

 manner. 



In Uiniilo as well as in Aitlastovuon the orifices of the glands 

 which open upon the jaws are found hctweon the teeth. 



The teeth have somewhat the shape of a /^, the apex of which is 

 directed towards the surface. They may ho readily isolated by 

 meansof liquor potass;e. In Axlastmnuvi they are lari;er, and, as is 

 well known, much fewer in number than in HirutJo. The teeth at 

 the lower end of the arch of the jaw are not so well developed as 

 those in the middle. Xevertheless the two somewhat stout processes, 

 which are directed away from the pharynx, are wanting, so that 

 the teeth are here rejiresented by small conical structures. The teeth 

 are entirely enclosed by the cuticle. 



The clearest idea of these structures is afforded by serial sections 

 through the jaws. 



The leech is killed by being thrown into alcohol. The jaws are 

 then dissected out, placed in alcohol containing picric acid, for the 

 purpose of decak-ifyiiig the teeth and, after suitable preparation, 

 embedded in paraffin. In the case of Ilirudo it is then not difficult 

 to divide the jaw into series of sections perpendicular to the piano 

 of the jaw and perpendicular to its base. This may also be success- 

 fully carried out in the case of AuJastomiim^ although here, on 

 account of the small size of the object, it is not so easy to hit upon 

 the direction desired for the section when the jaw is enclosed in 

 paraifin. 



The terminal sections of the series do not show the details clearly. 

 The section here passes oldicjuely through teeth and cuticle. At the 

 level of the apex of the jaw, however, the transverse sections exhibit 

 the condition of the teeth and cuticle distiuctly. The cuticle, which 

 clothes the epithelium of the jaw, increases greatly in thickness 

 on the anterior and posterior surface of the jaw, so soon as it reaches 

 the free margin, and runs out in a sharp edge towards the pharyngeal 

 cavity. Between the cuticle of the anterior and that of the posterior 

 surface a cleft-shaped space is left, and in this space the excretory 

 ducts of the glands open. Each time that a tooth is encountered, 

 however, we find that this space is closed. The decalcified teeth 

 stain well with hteraatoxylin, while the cuticle remains free from 

 this colouring-matter. Consequently in the sections every part of a 

 tooth may be clearly distinguished from the cuticle. The tips of 

 the teeth do not project beyond the free edge of the cuticle. 



If an entire jaw, which is best not stained, be made transparent 

 by means of oil of cloves, and then mounted in Canada balsam with 

 the free edge uppermost and a suitably 8upf;orted cover-slip placed 

 over it, the sharp edges of the cuticle of the anterior and posterior 

 surfaces of the jaw can be observed quite distinctly as two fine lines. 

 The slit which is left between them is foiind to be open and closed 

 by a tooth in regular alternation. 



The teeth are consequently to be regarded as an apparatus for the 



