300 



KNOWLEDGE. 



Al'GUST. 1911. 



however, elapsing befc 



tlK 



strut: 



of the 



captured animal finallv cease. In the case of an 

 Entomostracan. the process of digestion being 

 completed, the hard indigestible shell is gradually 

 worked along to the surface of the body and 

 ejected, a depression appearing in the ectoplasm 

 at the place where the hard substance passed out 

 into the surrounding medium. 



The process of digestion is of a sonuw hat tardy 

 nature : in one case an interval of nearly t\\ enty- 

 four hours elapsed from the time an Entomostracan 

 was engulfed to the time the emjitx' shell was 

 ex[K'lled from the body. 



Waste matter is occasionally ejected from the bod\' 

 of the Acfitiospliacriiiiii. Sometimes this waste 

 material is enclosed in a bladder-like x'acuole which, 

 on leaving the bod\-, appears to glide along the 

 pseudopodia, finallv floating off into the surrounding 

 water where it gradually collapses, the contents 

 being dissipated. Occasionall\' these bladders are 

 suddenh- ruptured and the contents expelled with 

 some considerable amount of \-iolence. 



Another curious phenomenon in tlie life historv of 

 the Act inospliae rill III ma\- occasionalh' be witnessed 

 w hen two of these organisms slow 1\- approach one 

 another, cross their respective pseudopodia. and thus 

 united, glide slowly through the water. In a short 

 time the body substance of the tw(.) organisms may 

 also be seen to come into contact, ajjpearing as in 

 Figure 1. .\fter the lapse of about a quarter of an 

 hour, the two bodies apparently become completely 

 fused, as shown in Figure 2. their respecti\'e pseudo- 

 podia remaining, however, quite distinct, together 

 with the two centres from which they radiate, w bile 

 there appears to be a dividing line between the two 

 endoplasms. This dividing line soon, however, 

 disappears, the two endoplasms merge into one, 

 while all the pseudopodia are now seen to radiate 

 from a common centre, and in the course of about 

 an hour the two bodies have become as one, as shown 

 in Figure 3. The phenomena of cytotrop\-, or the 

 mutual attraction of two or more cells, are in all pro- 

 bability closely connected with conjugation, and 

 cytotropy, leading first to contiguity, may result in 

 plastogomy, or the fusion of plasms. The proto- 

 jilasm, however, must be in the proper plastic 

 condition for such a union, and some of the Heliozoa 

 are apparenth" alwa^'S in this condition and contact 

 results in fusion. In many cases, however, plasto- 

 gomy leads to nothing further, and no nuclear 

 fusion takes place. 



Occasionalh' two large Actiiiospliaeriu will unite 

 and form a body as shown in Fig. 4, large 

 spherical vacuoles being visible in the bod\- substance. 

 .\fter remaining in this condition for some hours the 

 two bodies gradually round off into the form of a 

 perfect sphere, .\gain, it sometimes happens that the 

 two bodies, after remaining fused for some hours, 

 will separate, then appearing to ln' in the same 



condition as before the fusion occurred. In other 

 cases, the two Actiiuisplujcria are seen to be united 

 by a narrow band of protoplasm as shown in Fig. 5. 

 In appearance this connecting band resembles an 

 elongated pseudopodium. the only difference being 

 that it is somewhat thicker, while in the centre thereof 

 is an expansion having all the appearance of a very 

 small Acfiiiospluicriiiiii. In a short time the band 

 connecting the organisms A and B (Fig. 5) parts, 

 leaving B, now rounded off into a perfect sphere, 

 still attached to C. Soon afterwards the band 

 connecting B and C is also severed, leaving B and C 

 floating in the water as separate organisms. 



It is [Possible tluit the abo\e-mentioned phenomena 

 form cases of plastogom\', and are not followed by 

 fusion of the nuclei as in true cases of conjugation, 

 although the latter has apparently been clearly 

 established in ActiiKi/^lirys sal. 



The Acfiiiospluicriiiin reproduces its kind by 

 means of binar\' subdivision, which is repeatedh' 

 performed under the protection of a cyst. 



In such a case the Actinosphaeriiiiit withdraws 

 most of its pseudopodia. while others coalesce and 

 protrude from the hod\' in the form of broadish 

 spikes. The ectoplasm appears to be very clear and 

 the vacuoles of large si^^e. while the endoplasm is dark 

 and opaque, and the w hole bod\" shows a considerable 

 decrease in size. In this condition it sinks to the 

 bottom of the (■(.•11 an(_l. after an interval of some 

 twelve hours, a kind of gelatinous substance 

 commences to form around it. On touching this 

 substance with the point of a very fine needle it is 

 found to be of a slimw sticky nature. 



The gelatinous covering graduall\- increases in 

 firmness, and under the protection thereof the body 

 substance of the Acfiiiospliaeriinu undergoes a process 

 of division until from ten to thirteen different parts 

 can be detected. 



Each separate part is of a dark colour and is 

 surrounded b\- an outer layer of some substance of a 

 clear transparent nature. These \'arious parts repre- 

 sent the \oung Actiiiosphaeria, which, after remaining 

 in this condition for varying lengths of time, finally 

 break through the cyst and soon acquire the likeness 

 of the parent form. It has been stated that the 

 Acfiiiosphaeriiiin reproduces itself by simple fission, 

 the cell slowly separating into two parts, and it is 

 further said that, should these organisms be kept for 

 some time without food and then be provided with a 

 superabundance thereof in the shape of Stentors, 

 they will multiply rapidly by division. 



However this may be, close observation of these 

 organisms has never shown the Actiiiospliaeriiini to 

 undergo di\ision save under the protection of a cyst, 

 while, furthermore, the introduction of Stentors into 

 the glass cell invariabh- caused the Actiiiosphaeria 

 under observation therein to withdraw their pseudo- 

 podia, being apparently quite unable to cope with 

 the powerful Stentors, 



