SEEING BY AID OF THE LENS. 



27 



is, then so are the zoospores which have 

 often been seen to issue from the cells 

 of an undoubted plant, and to dart 

 through the water, urged, much as / "ol- 

 vox is urged, by the vibratile action of 

 two or more cilia. That argument is 

 worthless. 



Another minute, motile organ con- 

 tained by the green peripheral bodies 

 (gonidia), is likewise difficult to see 

 unless carefully looked for, and even 

 then is readily missed, as eminent micros- 

 copists have done and have consequent- 

 ly denied its existence. Its presence in 

 undoubted animals, for instance in the 

 infusoria, the so-called "animalcules," is 

 readily observed, and readily accounted 

 for, as the recipient of at least some of 

 the water engulfed by the animalcule 

 when taking food, the latter as well as 

 the infusorian itself being continuously 

 and totally immersed. This organ is 

 the contractile vesicle, which has been 

 said to have no existence in plants, even 

 in nature's lowest and humblest. If, as 

 has been seriously stated, a contractile 

 vesicle is observed within a living object, 

 it follows that that object cannot be a 

 plant. Yet each gonidial cell contains 

 two of these minute organs, that regu- 

 larly and quickly contract, disappearing 

 entirely only to re-appear almost as 

 speedily in the same place. With twelve 

 thousand gonidia, each bearing two con- 

 tractile vacuoles, Volvox, let it be what 

 it may, is well supplied. But as Volvox 

 does not swallow solid food, as the in- 

 fusoria do, what function have these reg- 

 ularly pulsating spaces? One effect is 

 to puzzle the observing microscopist. 

 But as a feature by which to decide the 

 animality of the revolving, ciliated globe, 

 they are worthless, for the undoubted 

 zoospores of not a few microscopic 

 plants not only possess cilia, but pulsat- 

 ing vesicles that contract as rapidly and 

 as regularly as do those of Volvox. The 

 statement that no plant can have a pulsat- 

 ing vacuole may be safely rejected. 



But the gonidia contain still another 

 organ no less puzzling than those already 

 mentioned. This is the red, "eye-like 

 pigment spot."' Similar collections of 

 colored pigment are common in the in- 

 fusoria and the rotifera, in the last-men- 

 tioned animals sometimes being placed 



in contact with a distinct lens, which 

 may give the owner at least a glimmer- 

 ing of light, and so enable it to advance 

 toward the source. But what function, 

 if any, a similar pigmentary spot with- 

 out a lens can have a Volvox, is an un- 

 answered question. With motion, cilia, 

 contractile vacuoles and twelve thousand 

 "eye-spots," characteristics of common, 

 microscopic animals, Volvox becomes 

 an interesting object for serious study. 



Reproduction takes place in two ways, 

 each of which is complex and cannot be 

 described in a popular paper like this. 

 But as the result of one method, the 

 original sphere may contain within it 

 from eight to ten young spheres, much 

 smaller, but somewhat similar to the 

 parent, as shown in the accompanying 

 photograph, where ten are pictured in a 

 single maternal Volvox. These finally 

 escape through the ruptured surface of 

 the original sphere, the parent giving 

 her life for that of the young. 



In the photograph the small rings 

 which stud the surface are the green, 

 gonidial bodies. The cilia attached to 

 each one are not shown. To photo- 

 graph them with Volvox living and 

 actively moving, would be almost im- 

 possible ; to do so after it had been pre- 

 pared as a permanent "mount," for pre- 

 servation in a cabinet of microscopical 

 "slides," would be almost as difficult, 

 since soon after death they become flac- 

 cid, indistinct and difficult to be detected, 

 even by the eye aided by a good micro- 

 scope-objective. 



But is Volvox a plant or an animal? 

 Eminent microscopical botanists have 

 unanimously decided in favor of the 

 plant. But who knows what it reallv 

 is? 



ANNOUNCEMENT. 



Beginning with 1 the May issue, Miss M. 

 A. Booth, of Springfield, Massachusetts, will 

 take charge of a department of "Practical 

 Microscopy." Miss Booth was for many 

 years an editor of "The Observer" magazine, 

 and is well known to all who use the micro- 

 scope for serious scientific work or for 

 pleasure. 



