ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 601 



the aorta ventrally. The sympathetic plexuses in the walls of the 

 digestive tubes arise, not from the cells which migrate ventrally from 

 the sympathetic trunks, as earlier workers supposed, but from cells 

 which have their origin in the hind-brain and in the vagus ganglia. 

 These cells migrate peripherally along the vagi to their new location in 

 the walls of the digestive tube. The observations on Selachian embryos 

 cited by Held are shown to be inconclusive. They are based on 

 embryos in which the rudiments of the sympathetic trunks already 

 appear as distinct cell-aggregates. Embryos of Acanthias in this stage 

 of development are too old to reveal the exact sources of the cells 

 giving rise to the sympathetic rudiment. A large proportion of these 

 cells wander out precociously in embryos of Acanthias, and remain 

 scattered in the mesenchyme until they become aggregated to form the 

 " Anlagen " of the sympathetic trunks. The peripheral displacement of 

 the cells giving rise to the sympathetic nervous system cannot be 

 accounted for by the mechanical processes involved in growth or by 

 osmotic influences. Evidence is presented to show that the peripheral 

 displacement of sympathetic elements is probably determined by the 

 influence of hormones. 



The sympathetic nervous system in Fishes, like that in the higher 

 Vertebrates, is homologous with the other functional divisions of the 

 peripheral nervous system ; and the sympathetic neurones are homo- 

 logous with their afferent and efferent components. 



Early Development of Trout.* — Fr. Kopsch finds that the blasto- 

 meres of the egg of Salmo fario form at the middle of the fifth cleavage 

 a syncytium with one another and with the protoplasm which covers the 

 yolk. From this syncytial union segmentation-cells begin to separate off 

 from the end of the fifth cleavage onwards. This process of segmenting 

 off reaches, for the most part, its end at the close of the eleventh cleavage. 

 The nuclei that have arisen in the syncytium remain almost wholly 

 within it. The boundaries still present between the various territories 

 afterwards disappear entirely, so that the syncytium becomes a Plasmo- 

 dium. This is the time and the mode of origin of the yolk-sac entoblast. 



The segmenting off affects particular areas of the syncytium in 

 different ways. Thus there arise a marginal area and an eccentric area 

 (both with nuclei), and an intermediate area of the yolk-sac entoblast. 

 which has at first no nuclei or only a few. The place of the origin of 

 the yolk-sac entoblast is the margin and an eccentric area of the under 

 surface of the blastoderm. 



Development of Pectoral Fin in Amia.f — Ch. Heronimus finds that 

 the first primordium of the skeleton in the pectoral fin in Amia (as also 

 in Salmo) is an undivided plate. This stage lasts for a considerable 

 time. In the middle of the skeletal plate in Amia about seven clefts 

 appear at the same time. Later on another is added. At first the distal 

 and proximal margins of the plate are not divided. In Salmo the clefts 

 do not all appear at once. The elements in Amia increase to ten, but 

 there seem to be only nine in the adult. The facts lend no support to 

 the theory that the fin evolved by the transformation of any other organ. 



* Arch. Mikr. Anat., lxxviii. (1911) Festschr. Waldeyer, 2te Abt., pp. 618-59 

 (16 figs.). t Anat. Anzeig., xxxix. (1911) pp. 193-203 (8 figs.). 



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