i 4 THE LEECHES OF MINNESOTA 



are quite dull in color and some are bright and very attractiv. A few 

 of the color patterns are shown in the frontispiece and plate A. 



In most of the leeches one to five pairs of eyes, appearing as 

 more or less conspicuous pigment spots, are evident on the dorsal 

 side of a few of the anterior somites. Special sense organs, cald 

 sensillse, can be recognizd in most leeches on the dorsal surface 

 of one of the annuli of most of the somites. 



The body has no external appendages, such as antennae or 

 gills, excepting in a few species, not found in Minnesota; two have 

 external gills on certain somites. But the body is always coverd 

 with a thin, tough cuticle and more or less mucous. Some species 

 can secrete a large quantity of mucous in a very short time. 



The openings into the digestiv tract, the mouth and anus, usu- 

 ally are quite evident at or near the anterior and posterior ends 

 respectively. In the region of somites XI/XII, on the mid-ventral 

 line, there are two openings one to five annuli apart. The anterior 

 of these is the external opening of the male reproductiv organs and 

 the other is the external opening of the female reproductiv organs. 

 The excretory organs open to the exterior thru inconspicuous pores 

 on the ventral side of the somites containing them. 



When a leech is cut in two the body appears to be practically 

 a solid mass of tissue, the only conspicuous cavities being those of 

 the digestiv tract and some other organs. The digestiv tract and 

 other internal organs do not appear to lie in a distinct cavity as, 

 for example, do the intestin and some other organs of the chicken 

 or the frog. The body wall of the leech can be removd so as to 

 leave a compact mass of supporting tissue and embedded organs, 

 the whole presenting the general outline of the intact leech. In 

 other words, the space between the body wall and internal organs 

 and between the various organs is fild in with supporting tissue and a 

 characteristic vascular tissue. Consequently, in order to get a view 

 of the internal organs, this tissue must be carefully dissected away. 

 In Plate B are reproduced the fotografs of three successiv 

 stages of the dissection of one of our large leeches. In figure 1 only 

 the body wall has been loosend and pind out. The figure shows 

 that the supporting and vascular tissues so completely fill the space 

 between the various internal organs that none of the organs are very 

 evident. 



In the second stage of the dissection, shown in figure 2, the 



