HARDWICKE'S SCIENCE-GOSSIP. 



149 



membrane being ruptured only when comparatively 

 great pressure has been exerted upon the covering- 

 glass. The colouring matter of the eyespot, under such 

 circumstances, is seen to be a clear and apparently 

 semi-fluid substance, which, when examined with a 

 power bordering upon 2000 diameters, is perfectly 

 devoid of anything like granules or cells, and presents 

 an appearance of perfect homogeneity. 



The extreme delicacy of the flagellum and its 

 bulbous termination renders it very difficult accu- 

 rately to make out their structure. Nevertheless, 

 after a prolonged examination of them, and cautiously 

 watching the effects of what may be not inaptly 

 termed "transactional focussing," it would appear 

 that their structure is, at least, duplex ; the outer 

 membrane being much less opaque than the material 

 encased in it. 



Sometimes near the centre of the organism, but 

 oftenest near the tail, is a circular vesicle or vacuole, 



Fig. 86. — Various stages in the development of 

 Euglena viridis. 



the interior of which is of a much paler hue than the 

 rest of the body. This vesicle, however, does not 

 seem to be endowed with the power of contracting 

 independently of the whole body. But, as the state 

 of maturity is approached, and the " still" condition 

 is attained (at which time the flagellum disappears 

 altogether) a second vesicle developes very near to 

 the eyespot. This vesicle, or vacuole, possesses 

 the power of independent contraction. It is much 

 less than the one near the tail, being 'generally no 

 bigger than the eyespot itself; and its pallid hue 

 renders it almost invisible except under moderately 

 high powers. It certainly can be seen with a good 

 \ inch and No. 2 eyepiece, but its movements under 

 such a combination are very indistinct ; such move- 

 ments being best seen by an enlargement of about 

 2000 linear. The rate of contraction is nearly 



1 \ per minute. The systole is very sudden, but 

 the diastole is gradual, the combined action very 

 closely resembling the sudden collapse and slow 

 subsequent dilation of a vorticella. The presence of 

 this contractile vesicle is very significant, and is of 

 vastly more importance than the bulbed flagellum in 

 fixing the real position occupied by Euglena viridis 

 in the world of life ; and it goes very far towards 

 solving the somewhat vexed question, " Is the 

 Euglena viridis an animal or merely a plant ? " 



Had I not seen this contractile vesicle, and care- 

 fully watched its movements to make sure that they 

 were real, I should have been inclined to class the 

 Euglena viridis (as do the editors of the " Micro - 

 graphic Dictionary ") with Alga? ; but I cannot now 

 do so. Indeed, I feel no hesitancy in following the 

 lead of M. Lachmann and others, who, by virtue of 

 having witnessed the motions of this contractile 

 vesicle, ascribe a true animal nature to Etcglena 

 viridis. 



Several observers, and amongst them Mr. Slack, in 

 his excellent little book on the " Marvels of Pond 

 Life," speak of the rotifers and the higher infusoria 

 " greedily gulping down" these creatures. If this 

 be so common an occurrence as those observers would 

 lead one to infer, if the Euglena viridis in its various 

 stages of development forms one of the foodstuffs of 

 the inhabitants of the rotiferal and infusorial worlds, 

 I have been singularly unfortunate in my researches ; 

 for during the past eight months (a great part of 

 which time has been spent in the observation of these 

 organisms) I have never seen one of them, in any 

 stage whatever, swallowed either by rotifers or in- 

 fusoria ; although ferocious-looking monsters fre- 

 quently invaded the peaceful domain of the Eugleme. 

 Indeed, upon only two occasions have I seen within 

 the stomachs of animalcula anything at all resem- 

 bling them. My experience in this matter, however, 

 does not disprove the accuracy of the statements of 

 those observers to whom I have referred, as it is 

 quite possible that those voracious feedings may have 

 occurred during such intervals of repose as I have 

 found it necessary to take after several hours' con- 

 tinuous watching, and thus they may have escaped 

 observation. 



I append a sketch (fig. 86) of some of the " motile " 

 forms in various stages of contraction, with and 

 without bulbed flagellum ; and also the "still " form. 



Various forms of Euglena viridis. Nos. 1, 2, 3, 4, 

 5, show motile forms in various stages of contraction 

 with bulbed flagellum ; a, red eye-spot ; b, contrac- 

 tile vesicle ; c, non-contractile vesicle. No, 6, 

 shows motile form without the flagellum ; a, red eye- 

 spot ; b, contractile vesicle ; c, non-contractile 

 vesicle. No. 7 is the "still" condition of the 

 Euglena viridis ; a, red eye-spot ; b, contractile 

 vesicle ; c, non-contractile vesicle. No. 1 also 

 shows the granular appearance referred to above ; 

 with an enlargement of about 1500 linear, the 



