317 



DESMIDIE^E. 



DESMIDIE^E. 



318 



present this beak in frout of their body, as if it served to show them 

 the way ; but when they cease to move, by bending it back along the 

 side of their body, they resume the spherical form ; so that before 

 and after the motion one sees no trace of this beak. The motion of 

 the sporules before their exit from this point consists principally in 

 quick dartings along the walls of the articulation, knocking themselves 

 against them by innumerable shocks ; and in some cases we are almost 

 forced to believe that it is by this motion of the sporules that the 

 mamilla is formed. Escaped from their prison, they continue their 

 motion for one or two hours ; and retiring always towards the darker 

 edge of the vessel, sometimes they prolong their wandering courses, 

 sometimes they remain in the same place, causing their beak to vibrate 

 in rapid circles. Finally they collect in dense masses, containing innu- 

 merable grains, and attach themselves to some extraneous body at 

 the bottom or on the surface of the water, where they hasten to deve- 

 lop filaments like those of the mother plant." This process, to which 

 the name swarming has been given, has been observed by Mr. Ralfs, 

 Dr. Hassall, and others hi various species of Desmidieie, more especially 

 in fSfilueroplea criapa and Drapamauldia tenuis. No similar move- 

 meuts to these have been anywhere observed amongst the ova of the 

 animal kingdom. 



The presence of starch in the Deimidiecs 'is a third point relied on 

 by Mr. Ralfs as distinguishing the vegetable kingdom. The existence 

 of this substance is easily ascertained by the well-known reaction of 

 iodine upon it. Meyen first discovered this substance in the Algce, 

 and Mr. Ralfs and others have confirmed the correctness of his obser- 

 vations. At the same time it should be stated that starch, although 

 not found present in the tissues of the lower animals, has recently 

 been detected in the brain of man by Mr. Busk ('Microscopical 

 Journal,' vol. ii. p. 105). This tnay lead to the discovery of the 

 existence of this substance more generally in the animal kingdom 

 than has been hitherto supposed. 



1. 7>///^"/" M///I llorreri, with the cells uniting to form the preen matter. 

 2. Micrattfrvu crenata. 3. JZitattrttm "lili>rit/ttm. 4. Xarithidinnt armaturn. 

 5. The same with a frond acquiring a new segment by division. 6. Chtterium 

 Lltnuln. 7. I'fitiastrum timplex. 8. Pediaatrum llorynnum. 9. Ankistro- 

 tietinu* falcatlil. . 



The following reasons are given by Mr. Dalrymple, after giving an 

 account of the structure of Clatter ia, for placing the species of this 

 genus amongst animals : 



Int. That while C'lonterium has a circulation of molecules greatly 

 renembling that of plants, it lias also a definite organ unknown in the 

 vegetable world, in which the active molecules appear to enjoy an 

 iti.lc|,,.ti,l, tit motion, and the parietes of which appear capable of 

 contracting upon its contents. 



2nd. That tin' ;.''''" (,'elatinous body is contained in a membranous 

 envelope, which, while it is elastic, contracts also upon the action of 

 certain reagents, whose effects cannot be considered purely chemical. 



3rd. The comparison of the supposed ova with cytoblasts and cells 

 <.f plants precludes the possibility of our considering them as the 

 latter, while the appearance of a vitelline nucleus, transparent but 

 iiinlrriihir fluid, a <-lirinii, ur shell, determines them as animal ova. 



It was shown to be impossible that these eggs had been deposited in 

 the empty shell by other Infusoria, or that they were the produce of 

 some Entozoon. 



4th. That while it was impossible to determine whether the vague 

 motions of Closterium were voluntary or not, yet the idea the author 

 had formed of a suctorial apparatus fofbade his classing them with 

 plants. ^ 



On these reasons, Mr. Ralfs remarks, that the peculiar organ 

 the terminal globules of the Closteria are as much vegetable as 

 animal. That the throwing off the contents of the cell through 

 chemical reagents, is as much vegetable as animal. " If fresh water 

 touches Griffitltsia sftacea, the joints burst and spirt out their contents." 

 That the supposed ova contain starch, and are therefore vegetable. 

 That he cannot discover that the orifices at the extremities of some of 

 the Desm idiece are tubes, or that they possess a suctorial power. 



The Desmidiea are all of an herbaceous green colour, and from this 

 circumstance are easily discovered amongst the other microscopic beings 

 with which they occur. They are mostly inhabitants of fresh water. 

 Mr. Thwaites records two or three species from brackish water. They 

 are remarkable for the very definite outline which their forms assume, 

 especially in the genera Micrasterias (fig. 2), Euastrum (fiy. 3), Xan- 

 thidium (fly. 4), and Pediaitrum (flys. 7, 8). Their most obvious 

 characteristic however is their evident division into two valves or 

 segments. The point of union between the two segments is in 

 general very definitely marked. In Pediastrum and Scencdesmus it is 

 less obvious than other genera. It is at this point of union that the 

 cell opens and discharges its contents. " An uninterrupted gradation," 

 says Mr. Ralfs, " may be traced from species in which these characters 

 are inconspicuous to those in which they are fully developed : thus in 

 Closlerium and some species of Penium there is no constriction ; in 

 Tetmemorus, in some Cosmaria, and in Jlyalotkecu, it is quite evident, 

 although still but slight ; in JJulymoprium and Derniidium it is 

 denoted by a notch at each angle ; but in Sphcerozosma, Micraaterias 

 (fig. 2), and some other genera, the constriction is very deep, and the 

 connecting portion forms a new cord between the segments, which 

 appear like distinct cells, and are so considered by Ehrenberg and 

 others." He further adds, " That the frond in Euastrum (fly. 3) and 

 allied genera is really a constricted cell, and not a biuate one, will, I 

 am persuaded, be apparent to any one who traces the gradations 

 mentioned above." 



The manner in which the cells of the Damidiere are multiplied, 

 is by means of repeated transverse divisions. This process may be 

 seen in Euaitrum, the new segments appearing at the constricted part 

 of the original segments. At first the new segments appear as 

 two roundish hyaline bodies formed of the substance of the con- 

 necting tube. These lobules increase in size, acquire colour, and 

 gradually put on the appearance of the old portions. As they 

 increase in size the original segments are pushed away from each 

 other, and at length an entire separation takes place, each old segment 

 taking with it a new segment to supply the place of the old one. 

 This process is seen going on in Jig. 5. This process is repeated 

 again and again, so that the older segments are united successively, 

 as it were, with many generations. This multiplication however 

 has its limits, for the time comes when the segments gradually 

 enlarge whilst they divide, and at length the plant ceases to grow. 

 When this occurs no more segments are produced, the internal matter 

 changes its appearance, increases in density, and contains starch- 

 granules. The spore is now formed, which is to give birth to a new 

 individual, and the old one perishes. The separate cells formed by 

 this process of segmentation must be regarded as continuations of 

 the same individual. They are like the grafts and buds from a tree ; 

 they continue the individual. 



The reproduction of the Desmidieie seems to take place in two ways : 

 first, by the formation of granular contents in the cell, which have 

 the power of moving, burst the cell, and produce the phenomena of 

 swarming above referred to ; and secondly, by the formation of a 

 sporangium, or case containing spores, after the union or conjugation 

 of the cells before described. The sporangia assume a variety of 

 forms, and are sometimes covered with spines, and Mr. Ralfs says, 

 "That the orbicular spinous bodies so frequent in flint are fossil 

 sporangia of Desmidiece, cannot, I think, be doubtful, when they are 

 compared with figures of recent ones." 



Movements of the cell-contents of Desmidiece, similar to the cyclosis 

 of higher plants, have been observed by Dalrymple, Bailey, and 

 others. These movements consist of definite currents of the cell- 

 contents, passing in two opposite directions, the one along the side 

 of the cell, and the other along the periphery of the gelatinous mass 

 in their interior. Labarzewski, a German observer, states that these 

 currents are intermittent, lasting each time for about seven 

 seconds. 



The part fulfilled by the Desmidieai in creation is little known. 

 They undoubtedly purify the water iu which they live in the same 

 manner as other plants, and furnish food to a number of fresh-water 

 animals. As they do not attach themselves to external objects they 

 are seldom found living iu running streams. They are sometimes 

 found in the beds of large rivers, and several species are enumerated 

 by Drs. Lankester and Redfern, in their report on the ' Microscopical 

 Characters of the Water of the Thames.' The best places for 



