494 SUMMARY OF CURRENT RESEARCHES RELATING TO 



B. INVERTEBRATA. 



Structure of the Nucleus.* — J. Chatin has selected as objects of 

 his study the marginal cells of the Malpighian tubules of insects and 

 myriopods. After describing the methods of investigation, and 

 recommending the larvae of Diptera and Lepidoptera, he points out 

 that, at first, one rarely discovers all the details of the structure of 

 the nucleus ; as a rule, one only sees an enormous nucleus with from 

 two to five nucleoli and a fine filiform plexus. The different characters 

 presented by this last under ditferent conditions are then described 

 and discussed, and the nucleoli are described. 



The study seems to show that in the cells examined, as in certain 

 others, the nucleus is formed of a chief mass in which are found the 

 nucleoli and the plexus ; these one is at first inclined to regard as 

 secondary portions, but it is possible that the converse proposition is 

 the more exact and that the " somatic mass of the nucleus " is simply 

 a dependent of the reticulo-nucleolar apparatus. The nucleolus, 

 whether simple or multiple, appears to the author to be with diflBculty 

 separated from the plexus, or reticulum, and indeed the latter often 

 exists without the former. Chatin refers to the views of Klein in 

 whicli the " autonomy " of the nucleus is contested, but looks to further 

 observations for more satisfactory conclusions. 



MoUusca. 



Chromatophores of Cephalopoda.f — E. Blanchard was led to study 



these structures from the general consideration that there was some 

 mistake in the view which attributed colour changes in rejitiles and 

 fishes to amoeboid action, and to muscular influence in the Cephalo- 

 poda. As to the general structure of these parts in the Cephalojioda, 

 he finds no essential difference between them and the same bodies in 

 Vertebrates. The chromatophore is, in fact, a simple connective cell, 

 filled with pigment and possessing to a high degree the power of 

 amoeboid action ; the surrounding tissues do not aid it in its activity. 

 Those bodies are under the influence of the nervous system, but the 

 radiating fibres supposed to be connected with it are not, as Harting 

 has thought, nerve-fibres, but merely simple fibres of connective 

 tissue which have a special arrangement in the region of the chroma- 

 tophore, but have no connection with it. The author thinks that the 

 anatomical and physiological " anomaly " relating to these bodies in 

 the Cephalopoda must now be regarded as definitely denied. 



Development of Chromatophores of Sepiola.J — P. Girod, who has 

 already described the structure of the adult, now deals with develop- 

 ing chromatophores in Sepiola rondeletii. The embryonic cells below 

 the epidermis become differentiated into chromatophores and iridocysts. 

 The former arise from initial cells, which, growing and becoming 

 rounded, are the pigment-cells of the chromatophores. Each is 

 surrounded by four peripheral cells, and forms with them a chromato- 



* Ann. Sci. Xat. (Zool.) xiv. (1883) art. 3, 7 pp. (1 pi.), 

 t Bull. Soc. Zool. France, vii. (1883) pp. 492-6. 

 X Comptes Rendus, xcvl. (1883) pp. 1375-7. 



