

PROTOZOA ; INFUSORIA. 6/ 



and more diffluent sarcode, known as the " chyme-mass," or 

 " abdominal cavity." The " cuticle " is covered with vibratile 

 cilia, and is perforated by the aperture of the mouth. The 

 mouth leads into a funnel-shaped gullet, which is not continued 

 into any distinct digestive sac, but is lost in the central " chyme- 

 mass." Within the "'cortical layer "are the "nucleus" and 

 "nucleolus," and the " contractile vesicle" (or vesicles). The 

 nucleus is usually a solid band or rod-shaped body, having a 

 small spherical particle applied to its exterior, or immersed in 

 its substance. This latter is the so-called " nucleolus," which 

 must be carefully distinguished from the nucleolus of a cell, 

 which occurs in the interior of the nucleus. The contractile 

 vesicles are clear spaces, which contract and dilate at intervals, 

 and occasionally exhibit radiating canals passing into the sur- 

 rounding sarcode. Ordinarily one contractile vesicle is present, 

 or at most two, but in some cases there may be several. It 

 has also been maintained that the contractile vesicles com- 

 municate with the exterior of the body, but proofs are wanting 

 on this point. Whether this should ultimately be established 

 or not, there can be little doubt but that the vesicles are a rudi- 

 mentary form of vascular apparatus. Others, however, hold, 

 with some probability, that the contractile vesicles are to be 

 regarded as excretory in function, and that they correspond 

 more with the water-vascular system of the Annuloida then 

 with the true blood-vascular system of higher animals. Certain 

 other spaces termed " vacuoles " are generally visible in addi- 

 tion to the contractile vesicles. These, however, are probably 

 merely collections of water surrounding the particles of ingested 

 food, and performing with them a circulation in the abdominal 

 cavity, something like the circulation of granules which is seen 

 in certain vegetable cells. It was the appearance of these 

 " vacuoles " which are certainly not permanent organs of any 

 kind which induced Ehrenberg to term the Infusoria the "Poly- 

 gastrica," upon the belief that they were so many stomachs. 



Paramcecium obtains its food by means of the currents of 

 water which are set up by the constantly vibrating cilia. The 

 nutritive particles thus brought to the mouth pass into the 

 central abdominal cavity, along with the contents of which 

 they undergo the circulation above spoken of. Indigestible 

 and faecal particles appear to be expelled by a distinct anal 

 aperture, which is situated near the mouth. 



Reproduction in Parama>cium is effected either non-sexually 

 by fission (i.e. by a simple division of its substance) or by a 

 true sexual process. In this latter method two ParamKcia 

 come together, and adhere closely to one another by their ven- 



