CHAP. XIII.] INTRA-CELLULAR DIGESTION. 471 



Engelmann believed that he had obtained evidence that an acid 

 reaction is developed in Infusoria and some species of Amoebae 

 during digestive activity, and Meissner and Favre-Domergue are 

 said by Neumeister to have obtained similar results 1 . On the other 

 hand Miss Greenwood was unable by means of methyl-violet and 

 tropseolin, to determine the presence of an acid reaction either in 

 Amoeba or in Actinosphaerium. 



The observations of Metschnikoff 2 on the power possessed by the 

 colourless corpuscles of the blood to seize and disintegrate bacteria 

 and on which he founded his view of their function as phagocytes 

 bear the closest resemblance to those which we have been discussing. 

 Without further dwelling upon these, however, attention must be 

 drawn to the fact that Metschnikoff, Ray Lankester 3 and other 

 reliable observers ascribe powers of intra-cellular digestion to the 

 ^ndoderm and mesoderm cells of some comparatively highly differen- 

 tiated organisms, provided with an alimentary canal 4 . 



It appears to be a general law that a specialised digestive 

 mechanism, associated with the secretion of specific digestive 

 enzymes, is possessed by no parasitic creature inhabiting the alimen- 

 tary canal of its host a law of which examples are furnished 

 amongst Protozoa by the Gregarinae and amongst Vermes by many 

 Cestodes and by the Acanthocephali. 



" Complete degeneration of the gut is clearly due to adaptations to 

 definite modes of life, in which the food passes through the integument by 

 endosmosis. This phenomenon, brought about by parasitism, attains its 

 highest developement in the sporocyst forms of the Nematoda. Finally 

 the absence of an enteric canal is the rule among the Cestoda, where the 

 enteroii is not present for a time even. The enteron is altogether wanting 

 in the Acanthocephali, and for the same reason namely, parasitism." 5 



That these parasites possess an inter-cellular digestion seems to 

 be proved by their storing glycogen (M. Foster) which they probably 

 produce at the expense of the sugar and the soluble proteids which 

 they derive from their hosts. 



If we exclude Rhizopoda, Gregarinse and Infusoria, all non- 



1 M. Meissner, 'Beitrage zur Ernahrungsphysiologie der Protozoen,' Zeitsch. f. 

 ivissensch. Zoologie, Vol. XLVI. (1888); p. 498 and Favre-Domergue (Annales des Sciences 

 Naturelles, Zoologie, 1888, p. 140), quoted by Neumeister (Lehrbuch, etc. p. 115). 



2 Elias Metschnikoff, ' Ueber die Beziehung der Phagocyten zu Milzbrandbacillen, ' 

 Virchow's Archiv, Vol. xcvu. (1884), pp. 502526. 



3 Ray Lankester, Quarterly Journ. of Micr. Science, Vol. xxi. p. 123. The Author 

 has not been able to verify the quotation. 



4 Thus Metschnikoff asserts that the cells of the endoderm of Mesostomum and those 

 of the mesoderm of Synapta possess ingestive and digestive power, see M. Greenwood, 

 op. cit. p. 257 and Metschnikoff, ' Ueber die Verclauungsorgane einiger Siisswasser- 

 turbellarien,' Zool. Anzeiger, 1878, p. 387 and ' Untersuchungen iiber die intracellulare 

 Verdauuug bei wirbellosen Thieren.' Arbeit d. zoolog. Inst. in Wien, Vol. v. (1883), 

 Heft 2. 



5 Carl Gegenbaur, Elements of Comparative Anatomy, translated by Professor 

 F. Jeffrey Bell, M.A. The translation revised and a preface written by Professor 

 E. Ray Lankester, M.A., F.R.S. London, Macmillan and Co., 1878. Refer to pages 

 158 and 159. 



