18 



INTRODUCTION TO CLASSIFICATION. 



which stops short at the bottom of the funnel. The whole of the 

 bag formed by the cuticula is lined by a soft layer of gelatinous 

 matter, or "sarcode," which is called the "cortical" layer 

 (Fig. 5, A a) ; while inside that, and passing into it quite gradu- 

 ally, there being no sharp line of demarcation between the two, 

 is a semi-fluid substance, which occupies the whole of the 

 central region of the body. Neither in the cuticle, the cortical 

 layer, nor the central substance, has any anatomist yet dis- 

 covered a differentiation into cellular layers, nor any trace of 



Fig. 5. Paramcecium bursaria (after Stein) : A, The animal viewed from the dorsal side; 

 a, cortical layer of the body; 6, "nucleus;" c, contractile chamber; d d', matters 

 taken in as food ; e, chlorophyll granules. 



B, The animal viewed from the ventral side ; a, depression leading to 6, mouth ; 

 c, gullet ; d, " nucleus ;" d", " nucleolus ;" e, central sarcode. In both these figures 

 the arrows indicate the direction of the circulation of the sarcode. 



C, Paramcecium dividing transversely ; a a', contractile spaces ; 6 6', " nucleus " 

 dividing; c c', " nucleoli.'' 



that histological composition which we meet with in the tissues 

 of the higher animals ; so that here is another case of complex 

 vital phenomena proceeding from a substance which, in a histo- 

 logical sense, is structureless. 



At two points of the body (Fig. 5, A, c, e) the substance 

 of the cortical layer exhibits a remarkable power of contrac- 

 tion and dilatation. If you watch one of those points, the 

 sarcode suddenly seems to open like a window, and, for a while, 

 a clear space is visible, which then, quite suddenly, shuts again. 

 After a little time the same diastole and systole are repeated. 

 As the systole takes place, it is possible, occasionally, to discern 



