EXCRETED ELEMENTS. 



59 



by the intercalation of variously developed vacuolar spaces as to assume 

 a more or less complete reticulate or network-like character. Within the 

 ramifications of this central network, the granular sarcode with the enclosed 

 food-substances may or may not exhibit more or less regular circulatory 

 movements, the general appearances and attendant phenomena here, as in 

 the instances above cited, approximating again in a marked manner to 

 those which may be observed in various plants. Such a composition 

 and associated phenomena are, as pointed out by Professor Allman in 

 his recent Presidential Address to the British Association (Sheffield, 

 1879), especially observable in those plant cells with large sap-cavities, 

 met with in the stinging hairs of nettles, and other vegetable hairs, the 

 internal lining of which projects into the enclosed sap-cavity thin proto- 

 plasmic strings or filaments ; these, fusing with one another in various 

 directions, form an irregular network, along which under a high power of 

 the microscope a slow current of granules may be witnessed. As rightly 

 observed by Professor Allman, the vegetable cell with its surrounding 

 wall of cellulose is comparable under such conditions in all essential points 

 with a closely imprisoned Rhizopod ; the likeness, however, between a 

 highly vacuolate infusorium and such an internally modified vegetable cell 

 is still more striking.* 



Among the examples in which the central endoplasm has been observed 

 to exhibit motions other than circulatory, reference may be more especially 

 made to the type first described by Ehrenberg under the title of Monas 

 vivipara, here referred to the genus Spumella, and in which the entire body- 

 substance within the periphery exhibits under high magnification an active 

 vibratory motion of its enclosed granules that corresponds most closely 

 with the purely mechanical or " Brownian movements " of finely divided 

 inorganic particles. 



Excreted Elements. 



Under the above heading have to be assembled all those excreted pro- 

 ducts whose function it is to provide an external protective envelope for the 

 defence of the enclosed animalcules, and the majority of the variously 

 modified pedicles and other fulcra for support possessed by certain of the 



* An independent observation in a similar direction has recently fallen within the author's expe- 

 rience, the type in question being the elegant marine diatom Isthmia eitervis. The unicellular frus- 

 tules of this species, collected and examined in the living state at Teignmouth, Devonshire, in July 

 1879, were found to exhibit an exceedingly remarkable internal structure. The characteristic olive- 

 brown cell-contents or endochrome was found to be collected for the most part into a more or less 

 extensive central spheroidal mass, from which radiating and frequently branched granular thread- 

 like prolongations of the same substance extended to and united with the periphery. Submitted to 

 high magnifying power (700 diameters) both the central mass of endochrome and its radiating pro- 

 longations were shown to be composed of an aggregation of minute brown ovate or spindle-shaped 

 corpuscles immersed in or held together by a colourless and more fluid plasma. In the radiating 

 and reticulate extensions from the central mass these corpuscles were sometimes quiescent, but more 

 often were seen travelling in slow and regular order to and fro between the centre and the periphery ; 

 the general aspect under these conditions corresponded so nearly with the characteristic granule 

 circulation of certain Foraminifera and other Rhizopoda that it was difficult to realize that it wa> a uni- 

 cellular plant and not a Protozoon under examination. In the most actively moving cells almost the 

 whole of the ovate corpuscles were deployed upon, and in motion along, the radiating filaments, while 

 in the most quiescent examples both filaments and corpuscles were withdrawn into the central mass. 



