

VOLUTIUTHKS. 



VOLVOX. 



IMS 



body-whorl, which is carinated and nomewhat reflected, overhangs 

 both, *o a* to form an open somewhat rounded concavity. Pillar 

 4-plaitd. It U found on the African coasts in shallow water on lands 

 and mud. 



Cj/mba Ktptuni. 



m, MI from below, ihowinj the pUiU of the pillar ; t, ncrn from above ; 

 t, rouf Men from abort. 



VOLUTI LITH ES (Foil). [ VOLUTIDJL ] 



VOLVA, in PUuy, U the external membranous or flfahy covering 

 which inclom the itipei and pileus of the young state of many of 

 the order Pttngi. 



VOLVA'KIA. [VouiTiDJLl 



VOLVOX, a genus of organic beings referred by Ehrenberg to hi* 

 family of /n/wono. Siebold WM the first to doubt the correctness of 

 Ehrenberg' classification, and the result ha* been that through the 



subsequent retearehei of Williamson, liiuk, and Colin, the apecies of 

 \'olrn.r are now regarded aa forma of the vegetable kingdom. 



Ehrenberg describes three apeciea of Volmx: V.glubator, V.aurau, 

 and I'. tteUatut. A fourth form U described by Ehrenberg under the 

 name of Spluerotira Volrox. 



The following it Hr. Busk's account of these forma of Volvox : 



" The more common and bent known form of Volvox globalor, to 

 the naked eye, or under a low power, appears aa a transparent sphere, 

 the surface of which is studded with numerous regularly placed gre* n 

 granules or particles, and which contains in the interior several green 

 globules, of various sizes in different individuals, though nearly always 

 of uniform size in one and the same parent globe. 



"These internal globes, which are the young or embryo Volvox, 

 at first adhere to the wall of the parent cell, although the precise 

 mode of connection is not very apparent When thus affixed, they 

 are in a different concentric plane to the smaller green granules. At 

 a later period, and after they have attained a certain degree of develop- 

 ment, these internal globes become detached, and frequently exhibit 

 a rotatory motion, similar to that of the parent globe. 



" In the form of Volmx, termed V. aurcia by Khrenberg, the outer 

 sphere, or cell, exhibits precisely the same structure as the above, 

 the only apparent difference between them consisting in the deeper 

 green colour of the internal globules. These however soon exhibit a 

 more important distinctive character in the formation of a distinct 

 cell-wall of considerable thickness around the dark-green globular 

 mass. This wall becomes more and more distinct ; and, after a time, 

 the contents, from dark-green, change into a deep orange-yellow ; and 

 simultaneously with this change of colour the wall of the globulo 

 acquires increased thickness, and appears double. 



" The third form, or Volrox ttellaiiu, differs in no respect from the 

 two former, except in the form of the internal globules, which exhibit 

 a stellate aspect, caused by the projection on their surface of numerous 

 conical eminences, formed of the hyaline substance of which the outer 

 wall of the globule is constituted. The deep green colour of the con- 

 tents of these stellate embryoes, and their subsequent changes into an 

 orange colour, at once point out their close analogy with those of 

 V. aureiu. I have no doubt of their being merely modifications of the 

 latter : and in fact the two forms are very frequently to be met with 

 intermixed, and on several occasions I have observed smooth and 

 stellate globules in the interior of one and the same parent globe. 



" The organism described and figured by Ehrenberg, under the name 

 of ftjilttrroiira Volvox, also presents the appearance of a transparent 

 globe pet with green spots, but it differs from the foregoing in two 

 important respects : 



" 1. In the absence of any internal globules or embryoes. 



" 2. In the irregular size of the green granules lining the wall, which, 

 instead of being of a uniform size, are of various dimensions." 



Mr. Busk and Professor Williamson, in the first volume of the new 

 series of the ' Microscopical Society's Transactions,' have furnished in 

 great detail an account of the development of these curiously organised 

 granules. From their observations, it appears that the green ciliated 

 granules which stud the surface of the Volvox are produced from a 

 central embryonic mass of protoplasm by successive division by 

 segmentation. Mr. Busk observed in these green granules a curious 

 phenomenon. 



" It will also be observed, that each ciliated cell or zoospore, as it 

 may analogically be termed, contains a green granular mass or masses, 

 composed, for the most part probably, of chlorophyll granules and a 

 more transparent body, which I suppose may be regarded as a 

 nucleus, and derived, as it would appear, from one of the bright 

 spherules which have been noticed before. At an early period after 

 the maturity or completion of the zoospores they exhibit a minute 

 circular clear space, or sometimes, but I think rarely, more than one, 

 which is worthy of very attentive consideration. This space is of 

 pretty uniform size in all cases, and about l-9000th of an inch in 

 diameter. It may be situated in any part of the zoospore, or not 

 unfrequently in the base, or even in the midst of one or other of the 

 bands of protoplasm connecting it with its neighbours. Its most 

 important character consists in its contractility a property already 

 known to be possessed by similar spaces or vacuoles in vegetable 

 spores ; but what appears to me a very curious, and as yet unnoticed, 

 peculiarity of this contraction, consists in the fact that it is very 

 regularly rythmicaL In several cases in which I have watched the 

 phenomenon in question, uninterruptedly, for some time, the con- 

 tractions or pulsations occurred very regularly at intervals of about 

 38" to 41". In one case however, if I was not misled in the observa- 

 tion, the interval was about twice this, namely, 1' 25". The contraction, 

 which appears to amount to complete obliteration of the cavity of the 

 vacuole, takes place rapidly or suddenly, as it were, whilst the dilata- 

 tion is slow and gradual." This contraction of vacuolar spores has 

 since been observed by Colin in a nppcies of J'rotococctu. 



Mr. Busk thus sums up the result of his observations upon Volrox 

 ylobator : 



" 1. That it originates in an apparently nucleated discoid cell, 

 which is generated in the interior of the parent, and liberated in a 

 perfect though not fully matured form, within which are contained 

 similar germs. 



" 2. That the contents of thin apparently nucleated discoid coll, 



