98 THE MYXOMYCETES. 



It may be as well to pause here for a while to point out the 

 significance of these facts. The capacity of taking in solid food 

 is usually considered the prerogative of animals ; plants imbibe 

 their food in a liquid condition ; and Saville Kent, who insists 

 that the statement in this naked form furnishes a distinct line of 

 demarcation between the Animal and Vegetable Kingdoms, considers 

 that this one point, well established, decides the question. But if we 

 consider the difference more deeply, I do not see that it affects the 

 couti'oversy in any way. Why do plants usually imbibe their food in 

 a liquid form ? Because the protoplasm of plants has the habit of 

 KUiTounding itself with a wall of cellulose, in which are no pores 

 capable of admitting solid particles of even microscopically visible 

 size. Animals on the contrary have a mouth, by which they can take 

 in particles of various sizes according to the capacity of the opening, 

 or else, as in the Rhizopoda, their protoplasm is not surrounded by an 

 nnpermeable wall. In either case, however, the nutriment is reduced 

 to a liquid form, by digestion, before it actually enters and becomes a 

 part of the substance of the bodj'. 



If, then, we should meet with a plant in which the protoplasm was 

 naked, we should expect it to possess also the power of ingesting solid 

 food. It need not be said that naked protoplasm is met with in the 

 Vegetable Kingdom, as in all kinds of spermatozoa or antherozoids, and 

 the zoospores of Algae, and you will remember the curious observations 

 of Francis Darwin upon the protrusion of naked protoplasmic filaments 

 from certain glands on the leaves of the Teasel, and also from the 

 cells of the stem of Agaricu^ vmacnrius.* The real difticulty is 

 to explain why these fungi do not develop cellulose coats to their 

 protoplasm, not to account for their taking in solid food. The 

 flagellum, too, is nothing more than a minute thread of protoplasm 

 projected from the body, and is possessed alike by the gonidia of 

 Volvox, and most zoospores and antherozoids. 



Again, the possession of a contractile vesicle is urged as a proof 

 that these creatures cannot be plants. Saville Kent says that, 

 according to his observations, a rhythmically pulsating vesicle is 

 possessed by none but members of the Animal Kingdom. But here 

 there is a great temptation to reason in a circle ; first, to make the 

 possession of a contractile vesicle the criterion of animality, and then 

 to declare that none except animals possess one. There are, no doubt, 

 a few diificulties in the way. Our esteemed member, Mr. Wills, 

 (]uotes, though without actually approving it, the statement of Busk, 

 that the gonidia of Volvox, when young, possess one or more contractile 

 vesicles. Saville Kent tries to explain the origin of the state- 

 ment by the supposition that Uroglena was mistaken for Volvox. 

 But the zoospores of Peronospora, of Cystopus, of some Saprolegnieie, 

 of Ulothrix, of Chaetophora, of some Palmellacese, of Microspora 

 foccosa, and of Stigeoclonium tenue, etc., have also been observed to be 

 furnished with contractile vacuoles. f 



* " Quarterly Journal of Microscopical Science," 1878, pp. 74-82. 



+ Huxley, "Scieuce aud Culture," iip.lGl, 170, and '•Com ptesRendus," .Tnue 16,1879, 



