OF THE PHYTOZOA. 119 



voluntary, or the result of volition, any more than the marvellous motion of 

 the leaves of Dioncea rnuscipula. 



Peocess of Nutrition-. — The process of nutrition of Phytozoa is of the 

 most simple kind ; and no valid evidence can be adduced in proof of the com- 

 plex polygastric organization represented by Ehrenberg. In fact, an apparatus 

 of stomach-sacs could not, by any analogy, be presumed in a set of beings 

 destitute of mouths ; and Ehi^enberg was unable to demonstrate, even to his 

 own satisfaction, an oral aperture, except in a very doubtful manner and in 

 a very few instances. What he took to be gastric cells are no other than 

 vacuoles and clear vesicles — sometimes the chlorophyll-cells ; the last, how- 

 ever, were more commonly assumed to be ' testes.' To support his behef in 

 the presence of stomachs, and also of a mouth at the anterior clear space, 

 particularly Avhere there is a j^rojection of the protoplasmic mass, the Berlin 

 natm'alist appealed T\ith most confidence to his experiments in feeding with 

 coloured substances. By this means he believed he demonstrated such 

 organs in some Monadina, — but so rarely, amid a large number submitted to 

 experiment, and moreover in so few species, that much weight could not be 

 attached to the result, especially when it is considered how many difficulties 

 and doubts must arise where such very minute beings are concerned. Allow- 

 ing that particles of colour actually entered within the interior, and Avere not 

 merely adherent (a question which the magnifying powers of the instrument 

 Ehrenberg used could scarcely determine), it is even then much more rational 

 to suppose that their entrance was by mere mechanical causes (by pressure 

 or the like), than by the medium of a mouth. This interpretation is adopted 

 both by Perty and Leuckart, who describe the introduction of such particles 

 as possible, although, indeed, exceedingly rare in the more clearly vegetable 

 structui'es, the Diatomeae. The former mentions {op. cit. p. 61) three in- 

 stances in which he encountered foreign particles Avithin the substance of 

 Phytozoa ; but these would, instead of supporting, be really opposed to the 

 polygastric hypothesis. For instance, he discovered in a Peronema a species 

 of Bacillaria as large as itself, and consequently not containable within one 

 of the supposed gastric cells. 



In the case of the soft, illoricated minute Monadina, into which fine particles 

 have found their way, it is to be remembered that they are mere masses of 

 yielding protoplasm unprotected by a cuticle ; and further, we may, along 

 Avith Perty, reasonably presume that, in some examples of the entrance of 

 external matters, it has been effected much in the same way as mth the 

 Amoebce, by the soft substance overlying and then surroimding them. 



If a mouth and stomachs have no existence, it follows that nutrition must 

 be effected by imbibition — by endosmotic and exosmotic action — just as in any 

 simple vegetable or animal cells. Perty (op), cit. p. 62) adduces an experiment 

 showing that, to some Phytozoa at least, water rich in nutritive organic 

 material is necessary to their complete and healthy development ; for when 

 taken fi'om such water and placed in other quite pure, they dwindled in size, 

 although, curiously enough, they at the same time became more active. 



To complete what we have to say of their vital endowments (irrespective, 

 that is, of the reproductive functions), the Phytozoa seek the light ; and aU 

 their nutritive acts are carried on more actively under its influence. The 

 only exception is when, in the process of propagation, they are about to pass 

 into the ' stiU ' condition and to become encysted ; then they eschew the light, 

 sink out of sight, and recede to the bottom, or under cover of aquatic plants 

 or of theii' debris. Under the influence of light they exhale oxygen gas, 

 and the green colour is especially developed, — whilst when kept in the dark 

 they lose colour, become pale, and present few chlorophyll-particles. The 



