APPENDIX. 65 



believing- that the two products of division possess a different dura- 

 tion of life. 



The process of fission in the Diatomaceae seems to me to be 

 theoretically important, because here, as in the previously-mentioned 

 Monothalamia (Euglypha, etc.), the new silicious skeleton is built 

 up within the primary organism, but not, as in Euglypha, for the 

 new individual only, but for both parent and daughter-cell alike *. 

 If we compare the diatom shell to a box, then the two halves of 

 the old shell would form two lids, one for each of the products of 

 fission, while a new box is built up afresh for each of them. In 

 this case there is an absolute equality between the products of 

 fission, so far as the shell is concerned. 



NOTE n. REGENERATION. 



A number of experiments have been recently undertaken, in 

 connection with a prize thesis at Wiirzburg, in order to test the 

 powers of regeneration possessed by various animals. In all essen- 

 tial respects the results confirm the statements of the older 

 observers, such as Spallanzani. Carriere has also proved that 

 snails can regenerate not only their horns and eyes, but also part 

 of the head when it has been cut off, although he has shown that 

 Spallanzani's old statement that they can regenerate the whole 

 head, including the nervous system, is erroneous 2 . 



NOTE 12. THE DURATION OF LIFE IN PLANTS. 



The title of the work on this subject mentioned in the Text is 

 ' Die Lebensdauer und Vegetationsweise der Pflanzen, ihre Ursache 

 und ihre Entwicklung,' P. Hildebrand, Engler's botanische Jahr- 

 bticher, Bd. II. i. und 2. Heft, Leipzig, 1881. 



NOTE 13. 



[Many interesting facts and conclusions upon the subject of this 

 essay will be found in a volume by Professor E. Bay Lankester, 

 ' On comparative Longevity in Man and the lower Animals,' Mac- 

 millan and Co., 1870. E. B. P.] 



1 Cf. Victor Hensen, ' Physiologic d. Zeugung,' p. 152. 



2 Cf. J. Carriere, 'Ueber Regeneration bei Landpulmonaten,' Tagebl. der 52. 

 Versammlg. deutsch. Naturf. pp. 225-226. 



F 



