THE MYXOMYCETES. 93 



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 difficulties in the way. Oar esteemed member, Mr. Wills, 

 quotes, 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 Saprolegnieas, 

 of Ulothrix, of Chaetophora, of some Palmellaceae, of Microspora 

 Hoccosa, and of Stigeoclonium teniie, etc., have also been observed to be 

 furnished with contractile vacuoles.* 



Lastly, it may be objected that the power of amoeboid movement 

 is characteristic of animal organisms. But, here again, the Volvocinese 

 come to our aid. Archer, in 1862, observed the primordial cells of 

 Stephanosphasra (an Alga allied to Volvox) leave the hyaline sphere in 

 which they are usually contained, and move about the field exactly in 

 the manner of a green Amoeba. f In fact, although they moved, like 

 Amoeba, by extensions and retractions of pseudopodia, they went so fast 

 that they might have given even Litltamip.bn discus fifty micro-milli- 

 meters start out of a hundred, and yet have won the race. Various other 

 cases of the same kind are recorded among mosses, algas, fungi, etc.,J: and 

 Sachs instances the amoeba-like movement of the protoplasm which 

 escapes from a ruptured cell of Vaucheria, as similar in its character§. 



We left our Mj'xomycete in an amoeboid form, creeping over the 

 matrix upon which it grew, increasing by fission, and feeding perhaps 

 upon the bacteria and other organised substances in the fluid. In this 

 state it has received the name of Myxamoeba. Where one spore has 

 germinated there will probably be many more, and these, creeping 

 about, meet and unite with one another in gradually increasing 

 numbers, and at last form a mass, technically known as a plasmodium, 

 which is relatively of colossal size, and which creeps about in a 

 reticulate manner over the matrix. It sends out pseudopodia in 

 various directions, and retracts them again, just like a gigantic amoeba 

 or some species of Foraminifera. 



Moreover, this plasmodium consists of an outer denser transparent 

 layer not cootaining granules, and an inner granular mass in which 



* Huxley, "Science and Culture," pp. 164, 170, and '■Comptes Eendus," June 16, 

 1879. 



f " Quarterly -Journal of Microscopical Science," 1865, pp. 116, 185. 



t "Quarterly .Journal of Microscopical Science," 186-2, pp. 96-103. 



§ Sachs' Botaiiy, p. 41. 



! I have seen a plasmodium of Physaruin cinereiun, forming a patch of jelly- 

 like substance nearly as large as one's hand, which roamed about the surf ace of a 

 rotten stump for three weeks, and finally retreating to the base formed its 

 sporangia iu a tew hours. In a day or two the sporangia were ripe and dehisced, 

 and in a w^eek nothing was left but their bleached and empty bases. 



