ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 477 



fewer and remain more markedly in the vicinity of the original foci. 

 The difference between the two types is primarily a difference in the 

 metabolism-rhythm. 



Tunicata. 



Organ-forming Substances in Ovum of Ciona.* — J. Duesberg has 

 corroborated in Ciona Conklin's notable observations on the ovum of 

 Cynthia (Sti/ela) partita. In the fertilized but unsegmented ovum of 

 Cio7ia intestitialis, there are three differently coloured zones which are 

 characterized by the different distribution of the structural elements — 

 the fundamental substance, the vitelline substance, and especially the 

 plastosomes. The zones are organogenic, each giving rise to a special 

 primordium in the embryo. Different organs of the larva enclose sub- 

 stances which are recognizable in the living ovum, and already present 

 in ovo something of the localization they have in the embryo. 



The egg of Cio?ia shows in the vicinity of the vegetative pole at the 

 periphery of the egg a layer — a violet crescent — formed of extremely 

 crowded plastochondria. This corresponds to the yellow crescent of 

 Conklin. Secondly, there is a brown zone with few plastochondria and 

 much vitellus — the grey protoplasm of Conklin. Thirdly, in the 

 vicinity of the plastochondrial zone there is a clear zone surrounding 

 the pronuclei, with only a few plastochondria and vitelline granules — 

 the clear protoplasm of Conklin. There is a definite inequality in the 

 quantitative distribution of the plastosomes, and it is probable that the 

 plastosomes are the organ-forming substances. In the future muscular 

 cells of the tail of the larva and in the future neural cells the plasto- 

 somes are most abundant, and it has been shown elsewhere that the 

 plastosomes play an important part in the formation of myofibrils and 

 neurofibrils. Julin t comments on the importance of Duesberg's re- 

 searches. 



INVERTEBRATA. 



Mollusc a. 



Phagocytic Organs of Molluscs. J — L. Cuenot calls attention to the 

 frequent occurrence of fixed phagocytes, scattered or agglomerated into 

 organs, in Molluscs. They occur in very diverse situations. In Chito- 

 nidae, terrestrial Pulmonates, Aplysia, Scaphander^ and many Lamelli- 

 branchs, the phagocytes cover the fine arterioles of the liver. In Solen 

 marginafus they are accumulated in the labial palps, and form on the 

 fine ramifications of the artery of the palp lymphoid nodules, which re- 

 semble in structure the ovoid gland of starfishes and sea-urchins. In 

 Prosobranchs with one nephridium, fixed phagocytes envelop the 

 vascular lacunae of the kidney and the gills. In Cephalopods the fixed 

 phagocytes occur in the interior of the branchial lamellae. 



=^ Bull. Acad. Roy. Belglque, Classe des Sciences, 1913, No. 5, pp. 463-74 (6 pis.). 

 t Bull. Acad. Roy. Belgique, Classe des Sciences, 1913, No. 5, pp. 457-62. 

 t Resumes des Communications, 9e Congres Internat. Zool. Monaco, ser. 3, 

 p. 10. 



