Early Development of Haminea 



Ruth E. Leonard 

 Reed College, Portland, Oregon 



INTRODUCTION 



In this paper, which can be at best only a fragmentary account of 

 some of the very early phases of development, my purpose has been to 

 set forth some of the pertinent facts of early development as observed 

 in Haminea vesicula, a species of opisthobranchiate inollusk; and to dis- 

 cover, if possible, wherein lay any significant similarities or differences in 

 development between that and the other molluscs of the same class whose 

 embryology has been studied. 



Haminea vesicula is a marine Gasteropod of the order Opisthobranch- 

 iata. It is found in profusion in the waters of Puget Sound. The mate- 

 rial used in this study was obtained at the Puget Sound Biological Station 

 during July and August. 1916. The work was done entirely from pre- 

 served material. The eggs were killed in corrosive-acetic solution, stained 

 in acidulated Delafield's haematoxylin according to Conklin's method, and 

 mounted in balsam, under a cover-slip supported on glass rollers to permit 

 of rolling the egg at will after mounting. 



The habits of Haminea vesicula during July and August are those 

 characteristic of the breeding season, since these months cover a period of 

 great reproductive activity. I have been unable to observe the habits 

 during a period of reproductive quiescence. During July and August it 

 is littoral, appearing on the eel-grass and Ulva just below the low water 

 mark. The writer has gathered large numbers of the animals and of their 

 characteristic egg-masses from the under side of the Ulva at all times of 

 day. Eggs in the 1 -celled stage and apparently freshly laid were obtained 

 most plentifully between tlie hours of 5 A. M. and 9 A. M., and Haminea 

 is frequently found in the act of laying between these hours. However, 

 one of the animals was found laying as late as 11 :40 A. M., and continued 

 laying in the laboratory until 2:45 P. M. 



Frequently an individual was found laying on a comparatively isolated 

 piece of eel-grass or Ulva on which were as many as 7 other egg 

 masses, all containing eggs in the 1 -celled stage. No other adults were 

 present in the immediate vicinity. The question arises whether these egg 



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