340 GENERAL HISTOKY OF THE INFTJSOEIA. 



ble, since the phenomenon is one to be very frequently observed in animal- 

 cules e^ddently in full functional activity and uninjured, and because the 

 particles of food entering the interior assume their usual globular form (i. e. 

 acquire the characters given by Ehrenberg to his so-called stomach-sacs), take 

 their usual course, and do not accumulate in a confused manner wdthin a large 

 sac, such as the supposition in question implies. 



Microscopists are now agreed in representing this rotation to be confined 

 to a layer or stratum of the contents within the subtegumentary or cortical 

 lamina, and not to extend to the central portion, as Cohn represented (Zeitschr. 

 1851, p. 265). The current is from left to right, as we look down upon 

 the animalcule (XXIX. 25) under the microscope, and therefore is actually 

 the reverse, or from right to left, with regard to the animal itself. It never 

 changes its direction or course ; but its rapidity varies in different species, and 

 even in the same species under diiferent circumstances affecting its vitahty : 

 such are, among external conditions, hght, air, warmth, and food ; others, age, 

 the encysting and reproductive acts. Cohn observed that some particles in a 

 Paramecium Bursaria occupied 1^ to 2 minutes in making the circuit. In 

 Vorticella the current is slower. The stream is composed of a thin mu- 

 cilaginous matter, bearing in it numerous granules and molecules, fat- cor- 

 puscles, globules of food (the stomach-sacs of Ehren])erg), and the remnants 

 of alimentary matters in their passage to the discharging outlet. The chlo- 

 rophyll-corpuscles of the cortical layer, the nucleus, and the contractile vesi- 

 cles are not involved in the cmTent, unless, indeed, a few of the first named 

 when accidentally detached from their matrix. The nucleus lies more or less 

 within the stream ; and although moveable to a considerable extent at times 

 by the onward pressure of a bolus of food, it yet seems to maintain a con- 

 nexion with the subtegumentarj' lamina, and to escape being drawn into the 

 rotating current. Further, in the large Vorticelliyia, such as Ejoistylis and 

 Opercidaria, the mass of fat-corpuscles at the base of the body does not join 

 in the current ; and it m.ust be noted that the food-globules do not circulate 

 until they have lost the independent motion received by them on their pro- 

 pulsion from the extremity of the oesophagus. 



The most correct \dew, in our opinion, of the natiu'e of the rotating stream, 

 is that of Lachmann, who conceives it to be the nutritive fluid elaborated from 

 the food, — in a word, ^' chjnne." Such a fluid, analogy suggests to be needed 

 by the cortical and sarcode laminae over which it spreads itself, to supply ma- 

 terial for their renovation and rebuilding, and to compensate for the constant 

 waste consequent on the perpetual movements of the animal. And may 

 we not fiu'thor presume that this ciuTcnt also serves to bear away from 

 the lamina effete pai*ticles prior to their elimination, just as the blood 

 of higher animals serves both as a pabulum to the tissues and a channel for 

 the removal of their worn-out material ? Moreover, this circulation of a nu- 

 tritive fluid around the inner layer of the animalcule has its analogy in the 

 rotation of a similar fluid around the general abdominal cavity of the Ccelen- 

 terata, such as the Ilydi'ozoa and Actinozoa. 



Respecting the cause of this rotation of the contents, several explanations 

 have been broached. Some seeing in it a close similarity to the cyclosis of 

 plants, have attributed it to a like cause ; but what this is in vegetable cells 

 is anything but certain. According to some, the nucleus of the plant-cell is 

 the exciting force, since the stream seems to set out from and to retui'n to 

 the nucleus ; but this is not universally the case. Others, again, imagine cilia 

 to cover the interior of the cell- wall — but this is only an hypothesis, — whilst 

 others find in the functional activity of growth and nutrition, coupled with 

 the co-ordinate actions of light, heat, and chemical affinity, a sufficient cause 



