I70 ANDREWS. [Vol. VII. 



Finding the subject by no means exhausted, and judging new 

 observations were necessary, the following work was begun at 

 Wood's Holl, Mass., upon material obtained in 1889 and in 

 1890, while enjoying the opportunities offered by the United 

 States Fish Commission. This material was supplemented by 

 that obtained in previous years at several of the marine stations 

 of the Johns Hopkins University.^ 



From the examination of the eyes of many adults, supple- 

 mented by some observations upon the formation of eyes, it has 

 been possible to formulate a general idea of the simple eye of 

 the polychaetous annehds differing, as will be seen in the sequel, 

 from those above referred to, and at the same time not contra- 

 dictory to that account of the so-called compound eye of some 

 sedentary polychaetae given in a previous paper (this Journal, 

 Vol. V). 



II. EYES OF ADULTS. 



NEREID.E. 

 Nereis alacris Verrill. 



The remarkable epitoke form of this annelid is found sexually 

 mature early in July, and more abundantly in August and 

 September, at Wood's Holl, where it may be taken swimming 

 at the surface in great numbers in the evening and night, under 

 various conditions of tide and weather.^ 



In these individuals (Fig. i) the eyes are not only remarkably 

 large, but also occupy a very uncommon position, the anterior 

 ones not looking forward horizontally as is usual (Fig. 11), but 

 partaking of the general modification of the head, and being 

 thus directed downwards. 



It is to be observed that, as compared with the common 

 arrangement (Figs. 11, 5), the small labial palps are brought 



1 The nature of the material demands the use of many methods. Haller's liquid 

 gave good results in general, but for the refracting part, the mixture of sea-water and 

 HjSO^, as recommended to me by Professor Patten, was found excellent. Perenyi's 

 liquid was most useful, yet various liquids containing osmic acid are sometimes 

 necessary. 



2 This annelid was first described by Professor Verrill in 1873 as Nectonereis 

 megalops, then in 1879, with the discovery of a female form, referred to Nereis 

 megalops, and subsequently identified as the heteroneris state of the Nereis alacris, 

 taken in deeper waters. 



