13 



BIOLOGICAL CONDITIONS. 



ENEMIES. 



The two important biological conditions which were considered 

 were the enemies and the food of the oysters in the pass. As re- 

 gards enemies, the Calcasieu oysters are well off. Star fishes do 

 not occur ; the sheeps-head, although browsing among the jetty oys- 

 ters, is not a serious menace ; boring sponges are absent, and bor- 

 ing mussels and conchs are rare. 



The only enemy which was found in abundance, especially in the 

 jetty oysters, was the parasitic trematode, Bucephalus ciiculus. 

 This parasite, which has the form of a little worm with two long 

 horns at one end, is microscopic in size, although the tubes in 

 which it is formed can readily be seen with the naked eye. Buce- 

 phalus is apparently harmless to man, but Mr. D. H. Tennent 

 who has been at work on its life history at Beaufort, N. C, finds 

 that it is extremely destructive to oysters. He has also discovered 

 the second host of the parasite, for Bucephalus like the liver fluke, 

 passes different periods of its life in different animals. The 

 smallness of the parasite, its habits, and distributon, make the 

 suggestion of any remedial measures premature.* 



The food conditions were very difficult to study, and no satis- 

 factory results are deducible from the figures which have been 

 obtained. There are two reasons for this failure; in the first 

 place the natural economy of the pass and the Gulf was totally 

 upset by the freshet, and those marine plants which serve as food 

 for oysters were often unable to live and thrive in the water in 

 which the oysters themselves barely held on to life ; in the second 

 place, the only locality where oysters could be gotten with com- 

 parative ease was on the west jetty where they were procurable at 

 exceptionally low tides. These were not frequent enough to per- 

 mit a regular examination of the oysters, and if they had been the 

 results would have been vitiated by the fact that the examination 

 would have been made always at the same stage of the tide. 



In the stomach contents of the jetty oysters almost always four 

 species of edible diatoms, Pleurosigma spenceri, Eupodiscus radia- 

 tus, Navicula didyma, and Coscinodiscus perforatiis, were found. 



*I am indebted to Mr. Tennent for kindly allowing me to refer to his as yet un- 

 published notes. 



