297 



and illustrated with very bad figures , so tbat it takes some 

 trouble to forui a good idea of tbese organs. 



Tbe best descriptiou togetber witb illustrations are given by 

 Leuckart. 



A uarrow bole in the bottoui of the sucker leads into a small 

 space, in which the three jaws are to be fouud. Tbe jaws are 

 placed in a three radieal star round au opening, whicb is the 

 begiuuing of the pbarynx. The augles between the three jaws 

 are equal ; a dorsal and two lateral jaws can be distinguished , 

 which form the sumraits of three folds. By a more minute exa- 

 mination of the jaws we will see that those folds are to be con- 

 sidered as the primitive organs, on which afterwards tbe jaws 

 have originated , for these folds are found on all the species and 

 the successive development of the jaws upon tbem is to be fol- 

 iowed until they have obtained their largest size in the genus 

 Hirudo. 



In order to investigate the minute structure of the bead , 

 I made chiefly use of niicroscopical sections. The animals were 

 killed in alcohol of 96 procent, then put into alcohol to wbicb 

 is added picric acid , in order to dissolve the carbonate of lime 

 in the teeth (24 hours), then washed in pure alcohol and treated 

 successively with alcohol absolutus and benzol to be imbedded 

 at last in parafine. 



The sections (5 micron) were laid upon water, extended by 

 addition of hot water and kitted with or without albumine upon 

 the coverglass. 



The parafine was now solved in petroleumether and the sec- 

 tion stained with Böhmer's Haematoxyline and finally mouuted in 

 Canadabalsam. It was not easy to get well-stained preparations ; 

 as a rule they accept the staiu difBcultly. 



I tried Mayer's carmine, Picrocarmine, doublé staining with 

 Eosine and Haematoxyline; Kleinenberg's Haematoxyline, warmly 

 recommended for staining worms , gave me good preparations, 

 but with Böhmers Haematoxyline I got tbe best results. 



Overstaining duriuf? 24 hours and discolouring in alcohol aci- 



