SOME NOTES OX ACTINOSPHAERIUM EICHORXII. 



By EDMOXD JOHN HUNT. 



The study of the minute organisms inhabiting pond 

 and stream has ever proved a fascinating field of 

 research to the student of that world of teeming life 

 which the microscope has been instrumental in 

 bringing within the range of man's vision. 



Among the numerous forms of surpassing beauty 

 shown b\- the microscope to be contained in a little 

 water obtained from the weed-covered surface of 

 some sequestered pool. few. perhaps, can surpass in 

 general interest that veritable giant among its 

 compeers — the Actinospluieriiini eicJinniii : and the 

 following brief notes, the result of close observation 

 and studv of that interesting organism, ma\- possibly 

 pro\e of some interest to many students of pond life. 



Under the generic name, Actinophrys, .A.ctino- 

 sphaerium was formerlv ranked with the smaller 

 Heliozoon — Actinophrys sol — but is now dis- 

 tinguished as Actiiiosphacriiiin cichoniii. 



Regarded as a microscopic organism, the .4l///k)- 

 spliaeriiitn is found to be of comparati\ely large 

 dimensions ; for, while the size of Acfiiiophiys sol 



varies from 



to 



of an inch, that of 



Acfiiiosp/iacriiini is about yjjn of an inch. Indeed, 

 so relativelv large is its size that, on holding to the 

 light a small aquarium containing specimens of the 

 organism, it ma\- frequenth' be detected with the 

 naked e\e, appearing as a minute spherical speck of 

 a greyish colour, either King in the debris at the 

 bottom of the bowl, or suspended among the threads 

 of confervae which may be floating in the water. 



Although holding a lowh' position in the scale of 

 life, the structure of the Actiiiosphaeriitm yet shows 

 some advance on that of the Amoeba ; the lobose 

 extensions characteristic of the latter organism being 

 in the case of Actiiiospliacriiini differentiated into 

 thin ray-like pseudopodia, which, although cajiable 

 under certain conditions of being w ithdrawn w ithin 

 the body substance, are \'et, as a rule, more often 

 extended for the purposes of locomotion and the 

 capture of food. 



Placed on the stage of the microscope, under a lens 

 of low power, the Actinosphaerium is seen, like the 

 Amoeba, to consist of two layers, namelv, an outer 

 layer or ectoplasm, which is of a comparatively firm 

 consistencv, and an inner layer or endoplasm. 

 Viewed under a lens of fairly high power, the 

 ectoplasm is seen to be composed of a vacuolated 

 substance, some of the vacuoles being of large size. 



In appearance the ectoplasm somewhat resembles 

 the meshes of a net, the lines representing the meshes 

 containing minute dark coloured granules which are 

 in constant motion, while the interspaces appear, as 

 a rule, to be clear and colourless. 



Treated with an alkaline reagent these vacuoles 

 may be seen to coalesce. 



In the endoplasm the vacuoles are of smaller size 



than in the ectoplasm : globules and granules of 

 various kinds are present, and embedded in the 

 protoplasmic mass may be seen numerous spherical 

 bodies, each containing a dark-coloured substance. 

 These bodies represent the nuclei with the accom- 

 panying nucleoli, and in some cases the\' appear to 

 be present in \er\' considerable numbers. .As 

 previoush' mentioned, the ra\-like pseudopodia. 

 radiating from the bod\' in all directions, show a 

 considerable advance in structure on those of the 

 Amoeba, being apparentl\' formed bv an extension of 

 the ectoplasm, while running down the centre of 

 each pseudopodium is a structure having the apjaear- 

 ance of a minute rod. These rods extend into the 

 endoplasm. and in manv cases appear to abut on the 

 nuclei. Whatever may be the nature of the sub- 

 stance of which these rods are formed, and it does 

 not seem to be at all clearl\- understood, there can 

 be no doubt as to their being characterised bv a 

 remarkable condition of toughness and elasticitv. 



It sometimes happens that a free-swimming 

 infusorian has the misfortune to be caught on the 

 extreme end of one of the long pseudopodia, and, in 

 its violent struggles to free itself, will bend the 

 pseudopodium until the latter assumes the shape of 

 a bent bow. ha\ing much the appearance of a fishing 

 rod as seen in the hands of an angler playing a large 

 fish. In such a case the strain must be enormous, 

 and should the infusorian succeed in making its 

 escape, a contingency which not unfrequentlv 

 happens, the pseudopodium is seen to spring back 

 at once to its original position, apparentlv quite 

 uninjured by the severe struggle. 



Under certain conditions, as, for instance, when 

 transferred from one glass cell to another, the 

 Actinosphaerium frecjuentlv completely withdraws its 

 pseudopodia within the body substance, but the\- are 

 soon again extended on the organism being left for a 

 short time undisturbed. 



The pseudo[)odia are used for the purpose of 

 capturing food, and probably also as a means of 

 locomotion. 



In all the specimens under observation two and 

 sometimes three contractile vacuoles were always 

 present. 



These vacuoles expand very slowly, and when 

 fully dilated project beyond the surface of the body. 

 The outer walls then contract, presumably casting 

 out the fluid contents, although no passage through 

 which these latter could escape can be detected. 



In "The Microscope and its Revelations" Dr. 

 Carpenter, in speaking of the contractile vesicle 

 as seen in Actinophrys sol, says that " the cavity of 

 this sacculus is not closed externally, but communi- 

 cates with the surrounding medium, not. however, by 

 any distinct and permanent orifice, the membraniform 



298 



