No. 3. — Simple Eyes in Arthropods. By E. L. Mark* 



That portion of Mr. Locy's paper on the development of the spider f 

 which deals with the formation of the eye appears to possess importance 

 outside the objects of his special study. The discussion of the bearings 

 of his discoveries on the simple or monomeniscous eyes of Arthropods in 

 general, is the object of the present paper. 



Two irreconcilable views have been held of late with regard to the 

 origin of the retina in the simple eyes of Arthropods. The writers upon 

 the subject have been pretty evenly divided in opinion. Grenadier, 

 Lankester and Bourne, and Carriere have all claimed, more or less dis- 

 tinctly, that the retina was derived from the "hypodermis ;" while Gra- 

 ber, Lowne, and Schimkewitsch have clearly inclined to the opinion that 

 it was an outgrowth from the cephalic ganglia. It has been impossible 

 for either party to establish its views beyond debate, on account of the 

 absence of the proper embryological information. 



Grenacher ('79, p. 158) claims the ectodermic (hypodermal) origin of 

 the retina as duly established for certain cases, but admits that, although 

 highly probable, a similar origin has not been proved for eyes of the type 

 to which those of the spiders belong. He says : " Der zweite Punkt auf 

 den es wesentlich ankommt, betrifft die Herkunft des Retinaelementes. 

 Was diese anbelangt, so haben wir auch einige Beispiele kennen gelernt, 

 die uns in einer "Weise, wie kaum etwas zu wiinschen iibrig lasst, diese 

 Abstammung klarlegen ; nur schade, dass sich so wenige andere anfugen 

 lassen. Mit den ersteren meine ich die Augen der Qchwimmkaferlarven 

 (Figg. 1-10, Taf. I), die uns so evident als moglich nicht nur die Ab- 

 hangigkeit des Retinaelementes, sondern auch aller iibrigen Augentheile 

 von dem Integument, der Hypodermis mit Cuticula, erkennen lassen. 

 Damit ist aber fiir diese Thiere auch zugleich die Abstammung des Eeti- 

 naelementes vom ersten, ausseren embryonalen Keimblatt, dem Ectoderm, 

 gegeben. 



" Nicht so gunstig steht es mit den iibrigen Formen von Larvenaugen, 

 sowie den einfachen Augen der Spinnen und Insectenimagines. Wenn 



* Contributions from the Zoological Laboratory of the Museum of Comparative 

 Zoology at Harvard CoHege. No. XI. 



t Wm. A. Locy, Observations on the Development of Agelena ncevia, Bull. Mus. 

 Comp. ZooL, Vol. XII, No. 3, pp. 63-103, 12 pi., Jan., 1886. 



VOL. XIII. — NO. 3. 4 



