60 MANUAL OF ZOOLOGY. 



having a small spherical particle applied to its exterior. 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 surrounding sarcode. 

 It has also been maintained that the contractile vesicles com- 

 municate with the exterior of the body, but proofs are want- 

 ing on this point. Whether this should ultimately be es- 

 tablished or not, there can be little doubt but that the vesicles 

 are a rudimentary form of vascular apparatus. Certain other 

 spaces termed ' vacuoles ' are generally visible in addition 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 ' Polygastrica,' upon the belief that they were so many 

 stomachs. 



Paramoecium 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 Paramoecium 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 Paramoscia 

 come together, and adhere closely to one another by their 

 ventral surfaces. The ' nucleus,' which is truly an ovary, 

 enlarges, and a number of ovules are formed in its interior. 

 In like manner, the ' nucleolus ' of each, which is really a test-is 

 or spermarium, also enlarges, and develops in its interior a 

 number of fusiform or rod-like bodies, which are believed to 

 be spermatozoa. The nucleolus of each then passes into the 

 body of the other, the act of transference being effected 

 through the mouth. Contact of the two reproductive elements 

 then takes place, and a number of germs are produced, which, 

 after their liberation froih the body of the parent, are de- 

 veloped into adult Paramoecia. 



Vorticella is a beautiful flower-like Infusorian which is com- 

 monly found in fresh water, adhering to the stems of aquatic 

 plants. It consists of a bell-shaped body, or ' calyx,' sup- 



