EARDWICKE'S SCIENCE-GOSSIP. 



!I9 



tinually decaying. These corms frequently produce 

 lateral smaller corms in the axils of the leaf-scales, 

 like the "eyes" of potatoes. A very brief and 

 precise description of the development of the corm 

 is that of Henfrey, which is as follows : — " The 

 corm of Arum maculatum, examined in spring, ex- 

 hibits two lobes, with an intermediate constriction ; 

 they lie adjoined horizontally : the corm of the past 

 year is shrivelled ; the other is solid and at the 

 summit exhibits sheathing scales enveloping the base 

 of the erect flowering-stem. Opening the sheath, 

 which turns upwards, we see that the flower arises 

 from a terminal bud, while in the axil |of the leaf 

 arising below it, exists a bud which is destined to 

 swell up and form a new corm for the next season, 

 the oldest one meantime withering away ; so that 

 two generations with the rudiments of the third 

 always co-exist ; these generations may consist of a 

 greater number of individuals when additional conns 

 arise from the axils of several of the scales of the 

 parent corm." I may add that by carefully lifting 

 these corms from the earth the shrivelled remains 

 of several corms of preceding years may be found, if 

 this is performed with great care. 



Henry E. Griset. 



NOTES ON THE PARASITIC TENDENCY 

 OF ROTIFERS OF THE GENUS PRO ALES; 

 WITH AN ACCOUNT OF A NEW SPECIES. 



By Percy G. Thompson. 



NO more interesting facts are known in connec- 

 tion with any particular class of animals than 

 those having reference to the structure and habits of 

 the parasitic members which it includes. 



In the Rotifera, some species are permanently and 

 exclusively parasitic in or upon other organisms, 

 animal or vegetable, and present consequent modifi- 

 cations of structure often of great significance ; while 

 again, not a few forms assume a semi-parasitism for 

 mere temporary purposes of transport or alimenta- 

 tion, and these, as might be expected, exhibit no 

 very remarkable structural peculiarities. It is the 

 object of the present paper to present a few new 

 examples of this latter occasional parasitism. 



The genus Proales contains rotifers, some of which 

 have been long noted for the strangeness of habitat 

 and mode of life which they have chosen, in which 

 to play their part in the universal struggle for exis- 

 tence. Thus P. parasita has been recognised as an 

 inmate of the revolving spheres of Volvox globator 

 ever since the time of Ehrenberg, taking up its 

 abode permanently and depositing its eggs in security 

 within the crystal plant-globes. And P. Wemeckii 

 has been known for an equally long period as 

 characteristically inhabiting certain gall-like out- 

 growths upon the stems of various species of Vauch- 

 eria. These two are well-known instances of the 



tendency to parasitism in this genus ; I wish now to 

 mention certain others. 



Ehrenberg has stated that a sister-species of 

 Proales, P. petromyzon, occasionally occurs with 

 parasita in the Volvox spheres ; this has never, to 

 my knowledge, been confirmed by any subsequent 

 observer, but is rendered all the more probable from 

 the fact that I have myself seen a third species of 

 this genus, P. decipiens, present within this alga. In 

 the latter case, adults and their deposited ova were 

 present together within the Volvox, and the Proales 

 appeared fully at home, nor did the spheres present 

 any appearance of being torn by forcible intrusion of 

 the rotifer ; no specimens of P. parasita were present 

 in any of the globes at the time. 



This same species {P. decipiens) I have seen also, 

 on one occasion, cosily ensconced within the partly- 

 decayed filaments of Vaucheria, thus usurping the 

 place of its ally, P. Wemeckii. The Vaucheria 

 thread contained so many developing ova (more than 

 a score) as to suggest that quite a series of adults had 

 been in the habit of frequenting it, while some half- 

 dozen individuals of decipiens, not long escaped from 

 the egg, roamed along the tube, poking about for a 

 way of exit. No galls were formed upon the alga 

 such as are produced by P. Wemeckii, the rotifers 

 and ova merely occupying an ordinary filament, 

 which had probably begun to decay before the 

 former entered into possession. 



The fact is that P. decipiens is eminently of a 

 grubbing disposition, making its way into any hole 

 or corner where decomposing matter — whether of 

 animal or vegetable origin does not seem to be of 

 consequence — is present, and there taking up its 

 abode for a longer or shorter while, until this rich 

 store of food-material is exhausted. I have thus 

 repeatedly seen it in situations where such de- 

 composition has been in progress, sometimes clean- 

 ing-out the shell of a dead water-flea, or again in an 

 alga-cell, in each case evidently with the same object 

 in view. Once I came across what I suspect to have 

 been this species, curled up inside the test of a living 

 rhizopod (Nebela collaris), in some sphagnum-water. 

 How the rotifer had effected its entrance was a 

 puzzle, for the Nebela's sarcode filled up the mouth 

 of the shell like a plug, leaving a large space within 

 the fundus in which the Proales lay, alive but inert ; 

 that the rhizopod was also living was proved by 

 slight movements of the protoplasm. Of course, the 

 rotifer may have been but the victim of the Nebela, 

 and have been engulfed as food — perhaps after a 

 desperate struggle for its life, succeeding in forcing 

 its way clear of the deadly living jelly into the cavity 

 of its assailant's shell ; but it is just as likely that the 

 rhizopod was the aggrieved party and the victim of 

 unlawful entry on the Proales' part. Other Nebela 

 shells were seen with rotifer ova within them. 



Proales pelromyzon, although usually met with 

 freely swimming, I have noticed playing the part of 



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