597 



Da die vorstehenden Auseinandersetzungen wesentlich zusammen- 

 hängen mit den Darlegungen, welche ich vor einiger Zeit über den 

 Bau des Nervengewebes gegeben habe, so nehme ich zum Schlüsse die 

 Gelegenheit wahr auf die umfassende Monographie von Nans en über 

 Myzostomum hinzuweisen, in welcher zum ersten Mal das Nervenge- 

 webe eines Wirbellosen mit Rücksicht auf meine Angaben der Durch- 

 sicht unterzogen erscheint i^. 



2. The Development of the Compound Eye of Orangen. 



By J. S. Kingsley, Sc. D., Maiden, Mass. 



eingeg. 14. September 1886. 



As I hope soon to publish a detailed account of the development 

 of the compound eye of Crangon, a mere outline is presented here. 

 Numerous figures illustrating every step in the process will be given 

 in the final article. 



The first rudiments of the compound eyes appear as circular pa- 

 tches on either side of the egg just after the gastrula stage. Each patch 

 is composed of a single layer of columnar cells, each cell having a 

 smaller superficial area than those of the surrounding blastoderm. 

 From near the centre of this circular plate an invagination takes place 

 and a small pouch of epiblast is pushed downwards, inwards and for- 

 wards under the infero-anterior portion of the optic plate, the posterior 

 part of which gives rise to the supra-œsophageal ganglion. The pouch 

 itself soon becomes separated from the parent epiblast and takes an 

 internal position, resting immediately on the yolk. By means of this 

 invagination three cell-layers are formed, to which, [for convenience 

 names may be applied. The external layer, the unmodified epiblast is 

 the epidermis ; the outer wall of the invaginated pouch which rests 

 against the epidermis is the retinal layer ; while the inner wall of the 

 same pouch (that resting on the yolk) is the ganglionic layer. 



From this condition there is but little change until the embryo is 

 well outlined and provided with the rudiments of seven pairs of appen- 

 dages. The optic cavity (cavity of invagination) remains distinct and 

 the cells and their nuclei retain their primitive appearance. Now 

 change is first noticeable in the nuclei of the retinal layer. They 

 have become more numerous and more columnar than those of the 

 epidermis. They rapidly elongate until their major axis is three or 

 four times as long as the minor one ; the whole layer still remaining but 



16 Fridtjof Nansen, Bidrag til Myzostomernes Anatomi eg Histologi. Med 

 9 Plancher. Bergen, 1885. 



