434 ALFRED GIBBS BOURNE. 



this object. Their function must remain for the present as a 

 matter for further investigation. 



2. Sensory Cells. — I do not propose to do more here 

 than draw attention to fig. 15, from Hirudo, showing 

 certain of these cells and their connections with nerve-trunks. 

 The preparation from which this is drawn was a section cut 

 with a freezing microtome and stained in gold chloride. 



My inability to say much upon this subject is the less to be 

 regretted since Leydig has dealt with these simpler tactile 

 bodies and their derivatives, the eyes, in a most detailed 

 manner.' In the same place he has given admirable figures 

 of the epidermic glands, both superficial and deep lying in 

 Hirudo. 



Subepidermis or Dermis. — Between the epidermic layers 

 and the regular circular muscles of the body wall is a layer 

 which varies in thickness in different genera, but exists, to some 

 extent, in all. This may be compared to the subepidermic 

 layer found in the skin of many animals, usually distinguishable 

 in the adult (where its development has been traced, the meso- 

 blast has been shown to enter largely into its composition) by 

 its vascular character. 



It is this layer with the superjacent epidermis which rises 

 into papillae in Piscicola, Pontobdella, and Clepsine, and 

 which constitutes the annular ridges in a contracted Hirudo, 

 Hsemopis, &c. It consists of a matrix of connective jelly ^ in 

 which are to be found the various forms of connective-tissue 

 cell to be described below, numerous and large blood-vessels 

 and short muscular fibres; the latter do not occur in Clep- 

 sine, Nephelis, or Trocheta, but are very fully developed 

 in Pontobdella (fig. 9, m. cut.), and serve to raise and 

 depress the papillae which occur upon the surface of the body. 

 In all the genera the branched ends of the radial and dorso- 

 ventral muscles (see infra, Muscular System, p. 435), 



> ' Vom Bau des thierischen Korpers,' 1864, and Atlas. 



* For these and some other terms, with regard to the connective tissue, lam 

 indebted to Professor Lankester's paper " On the Connective and Vasifactive 

 Tissues of the Medicinal Leech," ' Quart. Journ. Micr. Sci.,' 1880. 



