14 



PHYSIOLOGY 



CHAP. 



the microscope the behaviour and final modifications of the half 

 provided with, and that destitute of nucleus. When the operation 

 is effected with as little injury as possible, the edges of the cut 

 soon unite again, and each half of the amoeba contracts, assuming 

 a globular form. After a few seconds each of these two globules 

 begins to move, changing its shape and creeping along, as is the 

 normal habit of intact amoebae. Later on, however, a difference 

 between the two halves is perceptible, and while the new nucleated 

 amoeba continues to live and grow, and behaves as a normal 

 individual, the half without a nucleus slackens its movements, 

 takes no more food, retracts its pseudopodia, and, according to the 

 best results obtained by Hofer, dies in ten or twelve days. This 



proves the vital importance 

 of the nucleus. 



The second experiment, 

 designed to show the vital 

 importance of the cyto- 

 plasm, was carried out by 

 Verworn on a species of 

 Radiolaria ; Thalassicolla 

 (Fig. 2). In this animal it 

 is possible to shell out the 

 nucleus, separating it from 

 the ray -shaped mass of the 

 protoplasm, and to observe 

 the effects of isolation. 

 Even when the operation 

 succeeds without any per- 



iFio. 2. ThalassieoUa nudeata. (Verworn.) From CCptible llliclear lesion, the 



without, inwards: radiating corona of pseudo - ., 1 _.. ,-, iripvi tlbl V 

 podia: gelatinous layer; layer of vacuoles ; pig- J 



niented slicath to central capsule ; central capsule Without showing ailV 

 with nucleus. . ' " 



ot regeneration. 



A third experiment consists in bisecting a unicellular organism, 

 in such a way that each half contains a portion of the nucleus and 

 a portion of protoplasm. This succeeds readily in a trumpet- 

 shaped Infusorian called Stentor, in which both protoplasm and 

 nucleus are elongated (Fig. 3). When bisected each half 

 continues to live, and regenerates gradually into a perfect Stentor, 

 although of smaller dimensions. This fact cannot be adduced 

 against the theory which considers the cell as the lowest step in 

 the scale of living individuality, because each half of the divided 

 Stentor has the value of a cell containing the t\vo essential 

 constituents, nucleus and cytoplasm. It merely shows that the 

 living matter in the said cellular constituents may vary quanti- 

 tatively to a considerable extent, without forfeiting the conditions 

 necessary to the constitution of a complete individual. 



Just as a half-cell may live and regenerate into a complete 



