I.] APPENDIX. 6^ 



reproduce sexually, may remain alive for more than a week 

 waiting for a male : after fertilization, however, they lay their 

 eggs and die, while the parthenogenetic females of the same 

 species lay their eggs and die immediately after leaving the 

 cocoon ; so that while the former live for many days, the latter 

 do not last for more than twenty-four hours. 'The partheno- 

 genetic form of Solenobia triquetrella, soon after emergence, 

 lays all her eggs together in the empty case, becomes much 

 shrunken, and dies in a few hours.' (Letter from Dr. Speyer, 

 Rhoden.) 



Note io. Intermingling during the Fission of 

 Unicellular Organisms \ 



Fission is quite symmetrical in Amoebae, so that it is impos- 

 sible to recognise mother and daughter in the two resulting 

 organisms. But in Euglypha and allied forms the existence 

 of a shell introduces a distinguishing mark by which it is 

 possible to discriminate between the products of fission ; so 

 that the offspring can be differentiated from the parent. The 

 parent organism, before division, builds the parts of the shell 

 for the daughter form. These parts are arranged on the surface 

 of that part of the protoplasm, external to the old shell, which 

 will be subsequently separated as the daughter-cell. On this 

 part the spicules are arranged and unite to form the new shell. 

 The division of the nucleus takes place after that of the proto- 

 plasm, so that the daughter-cell is for some time without a 

 nucleus. Although we can in this species recognise the 

 daughter-cell for some time after separation from the parent 

 by the greater transparency of its younger shell, it is never- 

 theless impossible to admit that the characteristics of the two 

 animals are in any way different, for just before the separation 

 of the two individuals a circulation of the protoplasm through 

 both shells takes place after the manner described in the text, 

 and there is therefore a complete intermingling of the substance 

 of the two bodies. 



The difference between the products is even greater after 

 transverse fission of the Infusoria, for a new anus must be 



^ Cf. August Gruber, ' Der Theilungsvorgang bei Euglypha alveolata,' 

 and 'Die Theilung der monothalamen Rhizopoden.' Z. f. W. Z., Bd. 

 XXXV. and XXXVI., p. 104, 1881. 



F 



