PROTOZOA: INFUSORIA. 97 



contractile vesicles communicate 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 rudimentary form of vascular apparatus. 

 Others, however, hold, with some probability, that the contrac- 

 tile vesicles are to be regarded as excretory in function, and 

 that they correspond more with the water-vascular system of the 

 Scolecida than with the true blood- vascular system of higher 

 animals. Certain other spaces termed "vacuoles" are gen- 

 erally 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 circu- 

 lation 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 

 the vacuoles were so many stomachs. 



Paramozdum 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 fecal particles appear to be expelled by a distinct anal 

 aperture, which is situated near the mouth. 



Reproduction in Paramcedum may be effected non-sexually, 

 by fission, the body dividing transversely into two halves, and 

 the process of cleavage commencing first with the division of 

 the nucleus (fig. 32, B). Longitudinal fission is also stated to x 

 occur (fig. 32, C); but it is questionable whether the appear- 

 ances which have led to this statement may not really be due 

 to the coalescence and temporary conjugation of two indi- 

 viduals. Most authorities further believe that Paramadiim 

 has the power of true sexual reproduction, the "nucleus" 

 playing the part of an ovary in the process, and the " nucle- 

 olus " acting as a fesfis. In this process, as described by Bal- 

 biani, two Paramceda come together, and adhere closely to 

 one another by their ventral surfaces. The " nucleus " in- 

 creases in size, and a number of ovules are formed in its inte- 

 rior. In like manner, the " nucleolus " of each 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 trans- 

 ference being effected through the mouth. Contact of the two 

 reproductive elements then takes place, and the fecundated 



G 



