PROFESSOB W. a WILLIAMSON ON VOLVOX GLOBATOB. 337 



same influences. Though we have something approaching 

 to it in the case of the white cartilage cells of animals, I 

 have seen nothing like it amongst the undoubted infusorial 

 forms of animal life. 



In its globular form, the object approximates somewhat 

 to the well-known Ulva ghhosa. This little parasitic plant 

 has also a spherical contour, and consists of a saccated 

 membrane, on the under surface of which the numerous 

 cells are developed in a gelatinous intercellular substance. 

 This membrane appears to be nothing more than the ex- 

 panded and condensed tissues of the primary cells. I have 

 frequently found, that when it has been ruptured, the in- 

 ternal cells have floated out, when its cavity has become 

 filled with Naviculae and other minute Diatomaceae. 



The Volvox exhibits a still closer affinity to the Botridina 

 vulgaris of Brebisson, both in its structure and mode of 

 growth. This latter plant, like the Volvox^ is spherical, 

 being primarily developed from a single independent cell ; 

 only this cell if. solitary in the first instance, and not aggre- 

 gate. It develops in its interior a number of other cells, of 

 which those occupying its centre are subsequently absorbed. 

 *'The whole frond is then constituted of vesicles, closely 

 heaped together, and inclosing in the centre, granules. The 

 primitive membranej inclosing in its midst the interwoven or 

 cellular structure, is so closely united with the peripheral 

 stratum, of vesicles, that it can in no way he separated from, 

 it. The last development having been accomplished, the 

 peripheral stratum of vesicles altogether loses its granules. 

 Whether these disappear by absorption, or escape out- 

 wardly, 1 have never been able to perceive." Such is the 

 description of Botridina given by Meneghini, as quoted by 

 Mr. Hassal {British Fresh-water Algce, vol. i. p. 320). In 

 every point it exhibits so close an approximation to what 

 occurs in the Volvox, as to leave no room to doubt that 

 a close affinity exists between them. 



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