That beautiful animalcule: Andrew Pritchard on Volvox

Pritchard figure

Plate from Pritchard 1834. Image from Google Books.

Andrew Pritchard’s 1834 book The Natural History of Animalcules includes several species he classifies as Volvox. Most of them were probably not Volvox, but his Volvox globator certainly was. His description of Volvox begins on page 39. A scanned version is available online at The Biodiversity Heritage Library, but I have used the slightly higher quality scan in Google Books for the plate above.

The animalcules belonging to this genus are of a globular form, and revolve in the water. Some of the species are so large as to be discerned by unassisted vision, while others are very diminutive. Ehrenberg has not demonstrated their digestive organization; but in a note to his table, conceives they ought to follow the monads. In this genus is included that beautiful animalcule, called the Volvox globator, which forms so interesting a spectacle in the Solar and Gas Microscopes.

Volvox seems to have been a bit of a wastebasket for ciliated protists, many of which are clearly not volvocine. Interestingly, Pritchard has assigned common names to all of the species. His description of Volvox globator begins on page 46:

Volvox globator. The globe Volvox.–This popular and diverting animalcule was discovered by Leeuwenhoek, and has been described by all subsequent writers on microscopic objects. As its name imports, is of a globular form; its colour is usually a light green, though I have met with some of an orange brown, which, however are generally smaller than the green ones. The envelope is composed of a diaphanous membrane, beneath the surface of which is disposed, at equal distances, small spherical bodies of a green colour. These granular bodies have been supposed to reside on the exterior, and by some have been mistaken for hairs; but that they are actually within the envelope is evident when the circumference of the globe is accurately brought into focus. The proximity of these pustules is greater the younger the specimen, and as these pustules contain the colouring matter of the animalcule, the young always appear more coloured than the old ones, as the transparent spaces between the pustules is augmented in the latter, and spread over a greater surface.

I’m not sure what he could be observing that is “orange brown”; mature Volvox zygotes are often about this color, but I can’t imagine mistaking a zygote for a vegetative colony. As for the “granular bodies”, I suspect he is conflating reports referring to the cells and those referring to the flagella. The flagella match “mistaken for hairs”, and they are on the outer surface of the spheroid, while the cells could never be mistaken for hairs and are inside the spheroid. The description of the changing distances among “pustules” (cells) is dead on. Today we would describe that as an expansion of the volume of extracellular matrix as the colonies mature.

Within the parent is often seen a number of (from six to forty) smaller ones, and even within these, when about to be excluded, another generation may be observed. The young within the parent, which, by the way, forms the most striking characteristic of the species, may be observed at first attached to the inside of the membranous covering, but long before their birth revolving freely in the parent, and again others within them. In parturition, a portion of the parent globe is broken, and the young are gradually and slowly evolved; when this is completed, like the fabular Phœnix, the parent dies, and its body separates into numberless parts.

This singular animalcule, to use the words of Baker, “moves in all directions; forwards, backwards, up and down, rolling over and over like a bowl, spinning horizontally like a top, or gliding along smoothly without turning itself: sometimes its motions are slow, at others rapid.”

The diameter of this animalcule, when full grown, is about 1-30th of an inch, and is therefore easily perceived by unassisted vision: a magnifying power of 100 times is sufficient.

1/30 inch is about 850 μm, nearly a millimeter. Most Volvox species don’t get that big; those that do are mostly in section Volvox (aka Euvolvox), which does include Volvox globator. There’s no way of knowing whether Pritchard’s Volvox globator was the same species we call Volvox globator today, but it does seem to have been (at least) a close relative.

It is found most abundant, during spring and summer, in ponds and stagnant water; and often in the same water with young lizards and frogs. Infusions of hemp-seed and tremelia are said to abound with them.

Figure 22 represents a globe animalcule, magnified, with four smaller globes within it.

Here’s Figure 22 (also part of the plate above); sorry for the poor quality:

Pritchard Fig. 22

Figure 22 from Pritchard 1834. Volvox globator. Image from Google Books.

Pritchard’s Volvox morum may have been Pandorina, but the scans of the drawings are too poor to tell. From pages 44-45:

Volvox morum. The mulberry Volvox.–This group of animalcules differs from the former species [Volvox uva, Figure 15 in the plate] in the shape of the cluster, which is of globular form, like the fruit of the mulberry-tree, and the whole inclosed in a transparent membranous envelope. The individual globules, in which may sometimes be observed a slight motion, are usually of a bright sea-green colour, while th envelope which surrounds them is clear and pellucid, like glass. The cluster swims slowly, rotating as it progresses. They are found, during the latter months of the year, at the surface of ponds, covered with vegetation. Figures 16 and 17 represent two clusters of the mulberry Volvox, highly magnified: in the larger animalcule the internal cluster has been separated into several smaller ones, around each of which a separate envelope is about to be formed; it will then divide into six distinct clusters.


Stable links:

Pritchard, A. 1834. The Natural History of Animalcules: Containing Descriptions of all the Known Species of Infusoria with Instructions for Procuring and Viewing Them. London: Whittaker and Co. doi: 10.5962/bhl.title.8659

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