VOLVOCINE^E 5 5 i 



the water which it inhabits. Its onward motion is usually of a roll- 

 ing kind ; but it sometimes glides smoothly along, without turning 

 on its axis ; whilst sometimes, again, it rotates like a top, without 

 changing its position. When examined with a sufficient magnifying 

 power the Volvox is seen to consist of a hollow sphere, composed of 

 a very pellucid material, which is studded at regular intervals with 

 minute green spots, and which is often (but not constantly) traversed 

 by green threads connecting these spots. From each of the spots 

 proceed two long nagella, so that the entire surface is beset with 

 these lashing filaments, to whose combined action its movements 

 are due. Within the external sphere may generally be seen from 

 two to twenty other globes, of a darker colour, and of varying sizes ; 

 the smaller of these are attached' to the inner surface of the investing 

 sphere, and project into its cavity ; but the larger lie freely within 

 the cavity, and may often be observed to revolve by the agency of 

 their own nagella. After a time the original sphere bursts, and the 

 contained spherules swim forth and speedily develop themselves 

 into the likeness of that within which they have been evolved, 

 their coloured particles, which are at first closely aggregated together, 

 being separated from each other by the interposition of the trans- 

 parent pellicle. It was long supposed that Volvox is a single 

 animal ; and it was first shown to be a composite fabric, made up of a 

 repetition of organisms in all respects similar to each other, by Pro- 

 fessor Ehrenberg, who, however, considered these organisms as 

 monads, and described them as each possessing a mouth, several 

 stomachs, and an eye ! Our present knowledge of their nature, 

 however, leaves little doubt of their vegetable character ; 1 and the 

 peculiarity of their history renders it desirable to describe it in some 

 detail. 



Each of the so-called * monads ' (fig. 421, Nos. 9, 1 1) is a somewhat 

 flask-shaped plant-cell, about ^y^th of an inch in diameter, consist- 

 ing, as in the previous instances, of green chlorophyll granules diffused 

 through a colourless protoplasm, constituting an endochrome (which 

 commonly includes also a red spot ' eye-spot ' of altered chlorophyll), 

 and bounded by an ectoplasm formed of the condensed and colourless 

 surface-layer of the protoplasmic mass. It is prolonged outwardly 

 (or towards the circumference of the sphere) into a sort of colourless 

 beak or proboscis, from which proceed two nagella (fig. 421, No. 11) ; 

 and it is invested by a pellucid or hyaline envelope (No. 9, d) of 

 considerable thickness, the borders of which are flattened against 

 those of other similar envelopes (No. 5, c, c), but which does not appear 

 to have the tenacity of a true membrane. It is impossible not to 

 recognise the close similarity between the structure of this body 

 and that of the motile encysted cell of Protococcus pluvialis (fig. 

 418, K). There is not, in fact, any perceptible difference between 

 them, save that which arises from the regular aggregation, in Volvox, 



1 Professor Stein, however, in hit; great work on the Infusoria (Organismus der 

 Infusionsthiere, Abtheilung III., Leipzig, 1878), still ranks the Volvocinece among 

 the flagellate animalcules, to which they undoubtedly show a remarkable parallelism 

 in structure, the chief evidence of their vegetable nature lying in their physiological 

 conformity to undoubted thallophytes. 



