NATURE 



289 



THURSDAY, JANUARY 26, 1905. 



A MONOGRAPH OF THE HELIOZOA. 

 Les Hcliozoaires d'Eau Douce. By E. Penard. Pp. 

 341 ; illustrated. (Geneva : Henry Kundig, 1904.) 



THE Heliozoa or " sun-animalcules " have always 

 been favourite objects with microscopists on 

 account of their abundance, especially in fresh water, 

 their relatively large size, and their beauty as objects 

 for the microscope. From the scientific aspect, how- 

 ever, they have not attracted so much attention as 

 many other groups of Protozoa, on account, perhaps, 

 of their somewhat isolated position from the systematic 

 or phylogenetic point of view, no less than from their 

 perfect innocuousness, so far as mankind is concerned. 

 The work before us is a monograph of the fresh-water 

 Hehozoa, based upon investigations upon those found 

 In the environs of Geneva. It was the author's 

 original intention, he tells us, to have confined himself 

 to a description of the forms occurring in that terri- 

 tory, but since he obtained there nearly all the species 

 hitherto known from fresh water, he has added to his 

 catalogue descriptions of the species which appear not 

 to occur in the sphere of his personal investigations 

 in order to give his monograph a wider basis. 



The monograph is divided into four chapters. The 

 first contains general considerations on the structure, 

 reproduction, and affinities of the group; the second 

 gives a systematic account of those fresh-water forms, 

 the position of which among the Heliozoa is above 

 suspicion; the third deals with the " Pseudo- 

 Heliozoa," that is to say, with organisms commonly 

 referred to this group, but of which the affinities and 

 systematic position are dubious ; and the fourth dis- 

 cusses synonymic species, namely, those which are of 

 doubtful nature, or which have not been described in 

 a manner adequate for identification. The work 

 further commences with a short introduction and ends 

 with a full bibliography, and is illustrated by numerous 

 text figures. 



In his general chapter the author gives first an 

 account of the methods employed by him for collecting 

 these organisms, and then proceeds to consider their 

 body-structure. Under the latter heading he dis- 

 tinguishes two principal types of Heliozoa. The first, 

 or Actinophrys-type, has a large spherical nucleus 

 occupying the centre of the body, and lying, surrounded 

 by a clear zone of protoplasm, in the granular and 

 vacuolated endoplasm, which in its turn is enveloped 

 by the very vacuolated ectoplasm containing a large 

 contractile vacuole. The pseudopodia, seldom longer 

 than the diameter of the body, are supported by re- 

 latively strong axial filaments, centred round the 

 nucleus and radiating thence to the periphery of the 

 spherical body. To this first type, which might be 

 called the te.xt-book Heliozoon, mav be referred, 

 besides Actinophrys, the genera Clathrulina and 

 Hedriocystis, while xActinosphaerium is derived from it 

 by multiplication of the originally single nucleus. The 

 second or Acanthocystis-tvpe is much commoner ; here 

 the centre of the spherical body is occupied, not by the 

 nucleus, but by a central granule, apparently some- 

 what of the nature of a centrosome, from which radiate 

 NO. 1839, VOL. 71] 



the delicate axial filaments, each passing to the surface 

 of the body to be continued into one of the slender 

 pseudopodia, which usually exceed the diameter of the 

 body in length. The central granule and nucleus are 

 both contained in the endoplasm ordinarily so called, 

 which itself is eccentric in position, so that the sur- 

 rounding zone of ectoplasm becomes thin on one side 

 of the body and is thickest at the pole opposite to 

 this. The large nucleus is placed eccentrically in the 

 endoplasm, being always near the region where the 

 ectoplasmic zone is at its thinnest, and is therefore still 

 more markedly eccentric in relation to the body as a 

 whole. The author inclines to the opinion that the 

 ordinary use of the terms ectoplasm and endoplasm 

 is incorrect in the case of the Acanthocystis-type of 

 Heliozoon. He thinks that the true ectoplasm is here 

 limited to a narrow peripheral zone of the body, and 

 that the remainder of what is commonly called ecto- 

 plasm should really be considered as endoplasm, of 

 which that part to which the term endoplasm is usually 

 applied is only a special region, containing nucleus 

 and central granule, and perhaps homologous with the 

 clear zone round the nucleus in .\ctinophrys. 



In the classification the author keeps to the division 

 into the four well known orders founded by Biitschli, 

 and since repeated in every text-book, although he is 

 decidedly of opinion that this classification " is arti- 

 ficial and does not always correspond to the real affini- 

 ties of the species." If this is the case, it is a matter 

 for regret that the author did not attempt to embody 

 his ideas of the natural relationships of the Heliozoa 

 in a scheme of classification more suited to express 

 them. He contents himself, however, by making only 

 minor improvements, such as transferring the genus 

 Heterophrys from the Chlamydophora to the Chalaro- 

 thoraca. He also separates from Biitschli 's list certain 

 forms which are placed by him under the heading 

 " Pseudo-Heliozoa." This category, he is at pains to 

 explain, is not intended to have any systematic value, 

 but merely to serve as a mode of uniting " certain 

 organisms which exhibit points of resemblance to 

 Heliozoa sufficiently striking to tempt one to unite 

 them with the latter, and which nevertheless do not 

 belong to the group." Under the Pseudo-HeHozoa 

 are placed various aberrant types the descriptions of 

 which constitute one of the most valuable portions of 

 the book to the student of Protozoa. 



For the many interesting details of structure or 

 mode of life of these animalcules described by the 

 author the reader must be referred to the book itself. 

 The following sentences, however, from the section 

 headed " Psychology " merit quotation : — 



" If we wish to adopt the chemico-physical theory, 

 so much in favour now-a-days, according to which 

 everything in the lower beings is but mechanical re- 

 action, it is necessary to apply the theory consistently, 

 to examine the higher animals as well as the others, 

 and we shall then be forced to recognise that between 

 the top and the bottom of the psychical scale there is 

 only a descending gradation. Hence, according to 

 this theorv, the savant solving a problem should only 

 differ from the Protist in the greater complexity of the 

 physico-chemical reactions. If on the contrary one is 

 led to see something more than matter in the highest 

 manifestations of human thought, this something must 



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