164 



II. Wisseiiscliaftliclie Mittlieiliiiigen. 



1. The Development of the Compound Eye of Alpheus. 



By F. H. Her rick, I'li.D. Adelbert College, Cleveland, Ohio, U.S.A. 



eingeg. 4. Februar 1889. 



A Study of the embryology and systematic zoology of the crusta- 

 cean genus Alpheus was undertaken four years ago, and abstracts of 

 this work appeared in ISSO and 1887 ', when the development of the 

 compound eye received some notice. The most important details have 

 thus for some time been worked out, and the greater part of the draw- 

 ings have been ready for over a year, awaiting the publication of 



On. 



Y.5. 



Fig. 1. Transverse section through middle of left optic disc. Ch. = Chorion. 

 O.D. = optic disc. Y.S. = yolk spherule. 



the final monograph. Full illustrations are almost essential for a clear 

 presentation of the subject, but it is hoped that with the few figures at 

 our command, together witli those already published (see University 

 Circulars, No. 54), the following account may be fairly intelligible. 



The first trace of the eye in Alpheus is the optic disc (Kopflappen). 

 The embryo at this time consists chiefly of 3 patches of cells, namely, 

 the ventral plate, and anterior to this the optic discs, one on 

 each side of the middle line. Two germinal layers can now be recog- 



-^ 



o. 



iff^^îy 



^ 





Fig. 2. Transver.se section tlirough left optic disc, to one side of middle. The 

 thickening of the disc begun. 



nized, — an outer layer which we may call the ectoderm, and se- 

 condly an inner, indifferent layer, consisting of cells scattered 

 through the yolk. This last gives rise to all of the future endoderm, 

 to all or greater part of the mesoderm, and to some of the ectoderm. 

 The optic disc [O.D. Fig. 1) consists of a pavement or single sheet of 

 ectoderm, resting on the food yolk. From the optic disc the whole 

 eye, — that is the retina with its ganglia — is developed. 



' John Hopkins University Circulars, Nos. 54, O.'î. Baltimore, Maryland, U.S.A. 



