NATURE 



465 



THURSDAY, SEPTEMBER 17, 1891. 



ANIMAL CHLOROPHYLL. 

 Die Organisation der Turbellaria Accela. Von Dr. Lud- 

 wig von Graff. (Engelmann, 1891.) 



EIGHT years ago Dr. von Graff published his great 

 monograph of the Rhabdoccel Turbellarians. The 

 improved methods of histological research have enabled 

 him to add some essential facts since that date to our 

 knowledge of one of the most curious groups of the 

 Rhabdocoela — namely, those known as Acoela. In 1885 

 he passed his Easter holidays at the Franciscan convent 

 on the Dalmatic island of Lesina, and on the sea-shore 

 of the garden of the convent found Convoluta Schultzii 

 and cinerea in abundance. 



Prof. Delage in 1886 published his valuable researches 

 on Convoluta Roscoffensis^ the green species of Roscoff, 

 in which he made use of a method of gold-impregnation 

 for demonstrating the nervous system. Dr. von Graff 

 visited Roscoff in the same year, and in 1889 studied the 

 AccEla at the Naples Station by means of Delage's and 

 other methods of gold-impregnation. The present volume 

 deals with Proportis venenosus, O. Schm. ; Monoporus 

 rubripunctatus, O. Schm. ; Aphanostoma diversicolor, 

 Oerst. ; and several species of Convoluta ; it being shown 

 amongst other facts that the Roscoff species studied by 

 Geddes and Delage is distinct from the Mediterranean 

 C. Schultzii, and that C. cinerea, Graff, must be placed in 

 a new genus, Amphichoerus. 



The work is illustrated by ten quarto plates, coloured. 

 A variety of important anatomical and histological details 

 are given, and a systematic discussion of genera and 

 species. Dr. von Graff discusses the relationship of 

 Trichoplax to the Acoela, having received living speci- 

 mens of this curious form from the aquarium of the 

 Zoological Institute of Vienna, but he does not allude to 

 the Haplodiscus piger of Weldon {Quarterly Journal of 

 Microscopical Scicfice, vol. xxix.), a floating form, taken 

 off the Bahamas, which seems to be certainly a member 

 of the group. 



The chief matter of interest in Dr. von Graff's volume, 

 which we propose to notice at greater length, is the 

 chapter by Dr. G. Haberlandt, on "the structure and 

 significance of the chlorophyll-cells of Convoluta Ros- 

 coffensis." Dr. Haberlandt states that the description by j 

 Geddes of the chlorophyll of this form, as diffused in the \ 

 general plasma-body of certain cells, is erroneous. The ^ 

 green-coloured cells lie well below the cuticle, embedded I 

 amongst the cells of the superficial parenchyma. Accord- 

 ing to Haberlandt they are highly compressible and elastic, 

 and devoid of anything like a cellulose envelope or even 

 a membranous envelope. They are not uniformly green, 

 but there is as a rule a single large chloroplast which 

 forms a more or less complete shell to the protoplasm of 

 the cell-body. In some of the cells Haberlandt could 

 detect several peripheral plate-like chloroplasts. The 

 crust-like chloroplast contains as a rule a single centrally 

 placed pyrenoid of spherical form. As an exception two 

 or even three pyrenoids are present. The pyrenoid is 

 colourless ; it is stained by haematoxylin or by borax 

 carmine, but by no means so strongly as is the nucleus of 

 NO. 1 142, VOL. 44] 



the cell in which the chloroplast occurs. Starch granules 

 in the form of small curved rods are grouped around the 

 pyrenoid (sometimes within it), and are detected by a 

 violet-brown reaction on addition of iodine solution. The 

 colourless protoplasm of the cell is small in amount as 

 compared with the enveloping chloroplast : its nucleus is 

 only rendered visible by staining. The colourless proto- 

 plasm sometimes contains a group of granules of 

 doubtful nature, erroneously taken by Geddes for starch 

 granules. 



The resemblance of these cells, especially in respect of 

 the structure of their chloroplasts and pyrenoids, to cer- 

 tain cells which constitute the unicellular bodies of Volvo- 

 cineae, Tetrasporeae, and Pleurococcaceae, is insisted upon 

 by Haberlandt. He raises the question as to whether 

 they are to be regarded as parasitic Algae in the sense of 

 the theory of Entz and Brandt ; and suggests another 

 hypothesis — namely, that, whilst phylogenetically they 

 must be regarded as Algae (that is to say, have descended 

 from Algae), yet at the present time they have by pro- 

 found adaptation to life in and with the Convoluta, alto- 

 gether lost their character as independent algal organisms, 

 and have become an integral histological element of the 

 worm, and in fact constitute its assimilation tissue. 



To test this hypothesis he asks : (i) How do the green 

 cells get into the body of the worm ? and (2) What be- 

 comes of them when the worm dies ? Can they live in 

 an isolated condition ? To the first question he is unable 

 to give an answer, but suggests that they 7nay be handed 

 on from generation to generation of the Convoluta, enter- 

 ing the egg-cell as a colourless minute cell which later 

 develops its chloroplast just as the " leucoplasts " of 

 higher plants are found in the egg-cell, and later become 

 chloroplasts. As to the second question, Haberlandt has 

 no doubt. The green cells die when they are removed 

 from the worm's body or when the worm dies. He notes 

 in this connection their membraneless character, and 

 regards the loss of a cellulose envelope as one of the 

 modifications which the ancestral parasitic Alga has 

 undergone, rendering it incapable of living an inde- 

 pendent life away from the tissues of its host. Lastly, 

 Haberlandt justly remarks that siniilarity to an Alga is 

 no proof that the green cells are really Algae in nature. 

 Haberlandt is inclined to place his theory as to the green 

 cells of Convoluta alongside the suggestion of Schimper 

 as to the origin of the chlorophyll corpuscles of higher 

 plants — namely, that these are due to the union in the 

 remote past of a green-coloured with a colourless 

 organism. In this case and in that of Convoluta the 

 highest phase of symbiotic association is attained, for the 

 green organism can no longer be separated and cultivated 

 apart, as in the case of the Lichens, but has, in fact, 

 become an orga7i of the colourless organism, multiplying 

 with it and forming an integral as well as a necessary part 

 of its mechanism, and so greatly modified by ages of 

 association as to be now barely recognizable as derived 

 from an independent source. We can well suppose it 

 possible that the green cells of j^Convoluta might proceed 

 further in their modification, so as to lose the colourless 

 protoplasm and the cell-nucleus ; they would then become 

 simple chlorophyll corpuscles like those of higher green 

 plants. 



The suggestion thus put forward by Haberlandt is in 



X 



