520 SUMMARY OF CURRENT RESEARCHES RELATING TO 



layer of chrornatophores and iridocysts. The iridocysts are much- 

 branched cells with a central nucleus ; they contain bodies which reflect 

 the light and give rise to the rainbow appearance of the skin. These 

 the author calls iridosomes. The chromatophores can be distinguished 

 into two sets, according to the distribution of their pigment. In the 

 one — the vesicular type — the pigment granules are entirely peripheral, 

 and are arranged in a single layer round the large central cavity. In 

 the other or compact type the central cavity is absent and the pigment 

 is uniformly diffused. In the former the nucleus is peripheral, in the 

 latter it is central, and is remarkable in its staining reactions. The 

 young chromatophores are without pigment, and are only distinguished 

 by their size and their radiating fibres from the other connective-tissue 

 oells. In these cells the mother-substance of the pigment appears later, 

 and the pigment-granules gradually become differentiated in form and 

 colour. The vesicular chromatophores are only a stage in the develop- 

 ment of the compact form. The chromatophores are invested by a thin 

 cell-membrane, not by flattened cells, and the radial fibres are inserted 

 into this cell-membrane. The author believes that the radial fibres, 

 by their contraction, enlarge the chromatophore, while the elasticity of 

 the membrane contracts it, being assisted in the contracting process by 

 the pigment-granules themselves, which are capable of streaming move- 

 ments. The author denies the existence of the investing circle of cells 

 described by other investigators. Chromatophores are continually being 

 formed in adult cuttles, and there is a correlated degeneration of the 

 existing ones. 



Arterial Circulation of Nautilus pompilius.* — L. E. Griffin pub- 

 lishes figures and descriptions of the arteries of Nautilus, based partly 

 on his own dissections, and partly on the figures and descriptions of 

 Willey. He finds that the right side of the heart is slightly longer 

 than the left, so that it is not perfectly symmetrical. The so-called 

 auricles, which are merely distensions of the branchial veins, are not 

 morphologically equivalent to the auricles of Gastropods and Lamelli- 

 branchs. In some instances the branchial veins enter the heart without 

 showing any increase of diameter. 



y. Gastropoda. 



Variations of Planorbis.! — Franz Hilgendorf returns to the beauti- 

 ful results of his classic study (186G) of the transition from Planorbis 

 multiformis br acid for mis to Planorbis multiformis oxystomis. He re- 

 expounds his results, answers some criticisms, and furnishes a convincing 

 photographic plate. It is very satisfactory to have another utterance 

 from the veteran investigator of the Steinheim Planorbids. 



Evolution of the Gastropod Form of Body. % — Dr. J. Thiele returns 

 to a subject which he has discussed before, but it is difficult to make his 

 interpretation clear without illustrative figures. He seeks to show that 

 the shell could find a stable position only to the right of the apex ot 



* Circ. Johns Hopkins Univ., xix. (1900) pp. 53-6 (2 figs.). 



t Arch. Naturgesch., lxvii. (1001) Beiheft. Festschrift E. von Martens, pp. 331-40 

 <1 pi. and 1 fig.)- 



% Tom. cit., pp. 9-22 (4 figs.). 



