GROMIA 



339 



the very border line as between the plant and animal. It was long regarded as a plant, and it is only of late 

 years that testimony has accumulated in favour of its being an animal.^ 



Mr. Saville Kent traces a connection between the Mycetozoa and the Spongiidee ; the resemblance extending 

 to the fission or amoebic state, to the production in both of spores with flagella or cilia of some kind, to the encysted 

 or resting, hibernating condition, and to the presence in both of rudimentary skeletons in the shape of horn-like 

 elements or keratose, and spicule-like bodies of carbonate of lime. 



§ 64. Zooids and Monads. 



These are amongst the simplest of living animals. They have separate and combined existences. In other 

 words, they are sometimes found single either in the young or adult condition, and sometimes they are combined to 

 form colonies. The best examples occur in the Infusoria and in the Spongiidse, which have certain features in common, 

 as proved by the presence in all, in some shape or other, of 

 protoplasm, spores, flagella, cilia, &c. The protoplasm, spores, 

 flagella, and cilia are also met with in the embryo of the 

 Annelida, Echinodermata, Mollusca, and other invertebrate types. 



The presence in incalculable numbers in the air, in streams, 

 lakes, and the ocean of minute rudimentary plant and animal 

 forms is a subject of supreme interest to the reflective mind. 

 There is practically no limit to hfe, for the most minute living 

 object yet discovered by the aid of the microscope may be 

 resolved into its component parts and beginnings ; these being 

 molecular and invisible in their nature. The more rudimentary 

 and minute the plant and animal forms, the more persistent and 

 indestructible in many cases are they. These low types in their 

 germinal or sporular condition can successfully resist temperatures 

 which are fatal to higher organisms. They are proof against 

 boihng water and even higher degrees of heat. So far as ex- 

 traneous and cUmatic conditions are concerned they are practi- 

 cally indestructible. 



The mere minuteness of an organism does not limit or 

 determine its capacities and powers, and there can be little doubt 

 that unicellular plants and animals are capable of xmlimited 

 differentiation in the highest or ultimate sense, that is, in the 

 molecular sense. It is in the atomic and molecular region that 

 the organic meets the inorganic. 



It would be a hopeless task to attempt to deal even in a 

 general way with the coimtless multitudes of infinitely minute 

 and all but invisible rudimentary plant and animal forms. It 

 will be enough to state that they are each and all separate 

 individuals or entities, and reproduce only their own kind. I 

 propose, therefore, to describe very shortly, as representatives of 

 their class, only two of the unicellular organisms, namely, the 

 collared monad (Monosiga gracilis, S. K.) and the vorticella 

 (Vorticella nebulifera). 



The monad falls first to be considered. This simple, minute 

 rudimentary animal consists of the following parts : — 



(a) An elegant pear-shaped body supported by a slender 

 stem, by which it attaches itself to fortuitous objects. 



(&) A tapering vibratile hair or flagellum projecting from its upper end. 



(c) A delicate funnel-shaped frill or collar fixed to the upper part of the body and investing or surrounding the 

 flagellum. 



(d) A nucleus or endoplast. 



(e) Several contractile vesicles. 



1 "Manual of the Infusoria," by W. Saville Kent, F.L.S., F.Z.S., F.R.M.S. London, 1881. 



Fig. 74. — Collared monad (Monosiga yracUis), artiiicially 

 fed on carmine and greatly magnified (W. Saville Kent). 

 The animal consists of a pear-shaped body attached to a 

 pedicle or stem (broken off) surmounted by an elegant collar 

 resembling an egg-cup in shape [d). From the highest 

 portion of the body projects a flagellum or hair-like process 

 ifl), which by its varied movements creates currents in the 

 water, and causes the food particles therein to float into and 

 down the open collar (see arrows), where they are in a position 

 to be utilised by the body, fg, fg, Food granules ; cr, cv, 

 contractile vesicles ; 11, nucleus. 



