2 BULLETIN OF THE 



tions had been carried far enough to satisfy me that the retina in the 

 lobster was a simple ectodermic thickening. On returning to Cam- 

 bridge from Newport, the study of the lobster's eye was continued in 

 the Embryological Laboratory at Harvard College, under the direction 

 of Dr. Mark. Here I completed the observations on the development 

 of the eye, and studied its histology. In the fall of 1888 a brief pre- 

 liminary account of the results which are now presented in full was 

 published in " The Proceedings of the American Academy of Arts and 

 Sciences," Vol. XXIV. pp. 24, 25. 



In procuring at Newport the necessary stages in the development of 

 the lobster I proceeded as follows. 



Female lobsters with eggs were obtained from the fishermen, and 

 kept in floating latticed boxes which were anchored in the' small cove 

 beside the Laboratory. A few eggs were taken daily from each lobster. 

 The reagents which I employed in killing the eggs were Kleinenberg's 

 picro-sulphuric acid, Perenyi's fluid, a saturated aqueous solution of 

 corrosive sublimate, and hot water. The eggs which were prepared with 

 corrosive sublimate were rendered almost useless by the subsequent 

 formation of a fine precipitate. Those which were killed in Kleinen- 

 berg's picro-sulphuric acid and in Perenyi's fluid gave fair results ; 

 the latter reagent left the yolk in good condition for cutting. The 

 best results, however, were obtained by the use of hot water. Eggs 

 which had been prepared in this way could be easily shelled, and the 

 embryos could be readily dissected from the yolk. The separation of 

 the embryo from the yolk proved to be a great advantage, and obviated 

 the necessity of cutting the yolk, a tedious process in an egg as large 

 as the lobster's. 



In the following account of the development of the lobster's eye, the 

 stages which it is necessary to describe are taken from different sets of 

 eggs. These sets were from different lobsters, consequently I cannot 

 state with exactness their relative ages. I shall therefore characterize 

 them by their most evident structural peculiarities. Beginning with the 

 earliest stage and proceeding to the later ones, I have lettered them 

 A, B, C, D, E, and F. Set A is in the stage of the " egg-nauplius " ; in 

 this set the characteristic three pairs of appendages are easily distin- 

 guishable. In set B the thoracic appendages have begun to form. 

 This stage corresponds very closely to what Reichenbach ('86, Plate III. 

 Fig. 11) has designated in the crayfish as stage H. In stage C the 

 first trace of pigment in the retina is visible. Stage D is from the 

 same series of eggs as stage C, but is seven days older than C. In both 



