PROGRESS IN BIOLOGICAL INQUIRIES, 193 4 375 



as the controls. But the ciliary epithelium is very sensitive to the 

 oil extriut wiiich inhibits its action. Since the oyster feeds on 

 minute plants suspentled in water, the rate of feedin*; is directly pro- 

 portional to the volume of water i)umped throu*i:h the gills. 



There is no doubt that the presence of oil decreases the rate of 

 feedin<T; of oysters, and oil absorbed by coIloi(hil clay and deposited 

 on nuid bottom may exert its adverse effect on oysters long after all 

 traces of it have disai)peared from the surface of tlie water. 



Oil-well bleed water has an elfect on oysters similar to that of the 

 oil extract. 



Experiments with the diatom Nltzchia dosferia, grown under con- 

 trolled laboratory conditions, show that the rate of propagation is 

 decreased by oil floating cm the surface of the experimental flask and 

 by the addition of oil extract. From the results of the laboratory 

 experiments an inference can be drawn that both factors, the decrease 

 in the rate of feeding of oysters and the diminished production of 

 diatoms, create conditions adverse to the cultivation of oysters in the 

 oil-polluted areas. 



BIOLOGY AND CULTIVATION OF HARD-SHELL CLAM (VENUS MERCENARIA) 



AVhile certain phases of the life history of V. mercenm'ia are quite 

 well known, chiefly through the work of Kellogg and Belding, much 

 is still left to be learned about this animal, and there is a growing 

 demand for the information regarding the methods of its cultivation. 

 The aim of the study being conducted by V. L. Loosanoff at Milford, 

 Conn., is to obtain a broad knowledge of its life history, habits, and 

 physiology, and to develop practical methods of propagation. It is 

 expected that the results of this investigation will be instrumental in 

 devising methods for increasing the natural supply and for the 

 preservation of the clam fisheries. 



At present, the study is ccmfined to the following phases: Develo])- 

 ment and seasonal changes of gonads, spawning, development of the 

 ^^^^ growth, and feeding. 



The work along the first line consists in histological and cytologi- 

 cal studies of the material collected at regular intervals from the 

 experimental clam beds near Milford, Conn. The study is not quite 

 completed. It appears from the material examined so far that 

 the primary gonads of young clams are of protandric nature, that 

 is, the individuals first pass through the male phase. Whether the 

 Venus mevcenarm is strictly protandric or some of the individuals 

 mature as females wnthout the completion of a preliminary male 

 phase will be established upon the examination of more material. 

 Young clams 6 to 7 mm long already contain apparently functional 

 spermatozoa. 



Studies of the seasonal changes in the gonads of adult clams re- 

 veal processes which differ markedly from those observed in the 

 oyster. In the latter, after spawning is com])leted the gonad tissue 

 is absorbed, so that in the winter the gonads are in a well defined 

 resting stage. In Venus, a certain amount of absorption is also 

 evident, the principal degeneration of unspawned eggs takincr place 

 in December, but the gonad follicles do not shrink noticeably, and 

 well developed ovocytes are always present. In the male thesitua- 



