APPENDIX D. xci 



characters by the major part of the microscopists who have 

 observed them. Nevertheless, these forms, as well as the 

 particular size, which is often dependent upon accidental 

 circumstances, have no specific value. We shall see farther 

 on, that if a division into species can be established, it could 

 only have for its basis the mode of development, though 

 even this is found to be subjected to so many variations, 

 attributable to the modifications of the medium in which the 

 animals are found, that it would be more natural to admit 

 only a single species, and to consider as simple varieties 

 the slight differences which result from their mode of de- 

 velopment.' 



According to Lieberkiihn^ a relationship exists between 

 AmocbcE and Gregarincc which was previously unsuspected, 

 though similar in kind to the relationship described by 

 Carter between such organisms and Astasia:. He says- he 

 has seen the conversion of pseudo-NaviccllcE, that have been 

 undoubtedly derived from GregarincE, into Amoehce, and he 

 states that he has also met with every transition between 

 such AmcebcB and perfect GregarincE. The transition com- 

 mences by the case or cyst-like wall of each pseudo-Navicella 

 rupturing and giving exit to the soft contained matter, which 

 at first much resembles a minute Amoeba^ but gradually 

 assumes, by progressive growth and the formation of an 

 investing membrane around it, the characters of a Gregarina. 



There has been much dispute as to whether the Gregari- 

 nida are to be considered as independent organisms, or 

 merely as embryonic phases of other beings. Kolliker and 

 Leydig ^ have advocated the notion that they are metamor- 

 phic stages of certain nematoid worms. But even then there 

 is a further dispute as to whether the Gregarina becomes 



1 'Mem. de I'Acad. Roy. de Belgique,' 1854, t. xxvi. 



2 In 'Joui-n. of Microsc. Science,' vol. i. p. 208, some of Leydig's 

 arguments are given. 



