BULLETIN OF THE UNITED STATES FISH COMMISSION. 165 



testiue arises, making a couple of bends upon itself before opening 

 into the mantle cavity (mh). The entire internal surface of the alimen- 

 tary canal is clothed with cilia, with apparently the exception of the 

 hepatic diverticulum (/), the internal surface of which it is difficult to 

 observe iu consequence of the presence of a black pigment. 



At the point where the rudimentary foot was formerly developed, a 

 thickening of the ectoderm is now formed, of the same character as that 

 already described as arising in the center of the velar area. This mass 

 also contains a large number of nuclei ; but whether the pedal ganglion 

 is developed from it, I have not been able to make out, nor could I dis- 

 cover the presence of auditory vesicles, though Lacaze-Duthiers claims 

 to have seen them. Nor was I more fortunate in detecting the presence 

 of excretory organs, although I made special efforts to discover them; 

 otherwise the numerous points of agreement, of the larva (trochophora) 

 of the oyster with those presented by Teredo, were complete, with only 

 these slight exceptions. Perhaps renewed investigation would show 

 that the segmental organs also are not wanting. Older stages than 

 that represented in Fig. 12 I was unfortunately not able to investigate, 

 so that regarding the length of the period which intervenes between the 

 time when the larvos are set free, and the time at which they fix them- 

 selves, as well as the changes which they undergo during this period, I 

 am unable to affirm anything. 



The difficulties encountered in distinguishing the young oyster, im- 

 mediately after it has attached itself, I believe I have entirely overcome : 

 and instead of using the ordinary collector for this purpose, which is 

 covered with a mixture of lime and sand, a collector should be used 

 which is covered with an even coat of clean lime ; for the numerous 

 little asperities due to the presence of the sand grains; make it difficult 

 even for the sharp-sighted oyster fishermen to distinguish the shells of 

 the young oysters on the collectors of the usual form. In order to have 

 the surface as even as possible, I used panes of glass instead of the usual 

 form of collector, though this is not positively necessary. After one of 

 these panes of glass had been immersed in the water for eight days, 

 several young oysters were found to be attached ; of these the largest 

 measured mm .85 (about -fa inch), and the smallest scarcely mm .57 (about 

 4V inch) in diameter, though the latter was already visible to the naked 

 eye. 



The experiments instituted by Dr. De Leeuw and myself, in order to 

 learn if the young oysters would fix themselves in inclosed basins, have 

 not yet been completed. 



Before closing, I would call attention in this place to a probable 

 enemy of oyster brood. In my aquarium, in which a mother oyster 

 was placed, and which every now and then threw out a great quantity 

 of brood, there were also a couple of actiniae of the same species which 

 is very often observed attached to oyster shells. It occurred to me that 

 the quantity of brood was diminishing too rapidly, and upon making 



