748 I5ATUEAL HISTORY OF AQUATIC ANIMALS. 



shape of ' grouiid-ice ' or 'anchor-frost.' It is little understood, though often experienced, and I 

 was able to collect only vague data in regard to it. It appears that in hard winters the bottom of 

 the bgijs freezes solid in great patches, even at a depth of fifteen or twenty feet. The mud freezes 

 so hard that rakes cannot be pressed into it; and if a stronger implement, like a ship's anchor, is 

 able to penetrate it, the crust comes up in great chunks. These frozen patches are sometimes 

 forty feet square and continue unthawed for long periods. When such 'anchor-frost' takes place 

 at an Oyster-bed, of course the mollusks are frozen solidly into the mass, and few of them ever 

 survive the treatment. To the Cape Cod planters this is a serious obstacle to success."^ 



Interference op other animal liee. — We have called attention to the probable inter- 

 ference of small organic growths to the fixation of the young fry; in practice it is found that the 

 larger organic growths which establish themselves on the collectors also become injurious. The 

 two most conspicuous types are the sessile ascidians or tunicates and the barnacles. I have 

 frequently found .iully one-half of the surface of a slate covered with a dense colony of ascidians; 

 in this condition a great percentage of available surface is lost which ought to serve for the 

 attachment of spat. The surfaces so occupied would also be comparatively clean were it not for 

 these organisms, which actually become a serious annoyance. They, like the Oyster, affix 

 themselves to the slates while still in the free-swimming larval stage, since the surfaces designed 

 for the Oyster are equally well adapted to them. The barnacles, which also affix themselves in 

 great numbers, become a nuisance for the same reason. The larval barnacle is an extremely 

 active little creature, and dashes about in the water with great rapidity. As soon as it has 

 completed this stage of its growth it betakes itself to some object, to the surface of which it 

 attaches itself by the head end, when a singular change takes place, at the end of which it is 

 found that it has begun the construction of the curious conical shell which it inhabits. They 

 grow very rapidly, so that in a couple of months the shell will already measure over half an inch 

 in diameter. In this way further inroads are made upon the room which should be taken up by 

 Oysters, 



Of course the larger types are not alone in taking up space, since infusorians, bryozoans, 

 polyps, etc., are also culpable, as well as algae, such as diatoms and the higher forms. The only 

 remedy for this accumulation of animal growths on the surfaces of the slates and other collecting 

 apparatus will be to have the frames which hold the slate in position so arranged that each tile, 

 shingle, or slate can be removed, in order that it may be readily overhauled and these organisms 

 removed from the surfaces which it is desired shall remain clean. This work would have to be 

 done at intervals of every two or three weeks, and should be conducted with great caie, so as not 

 to remove the Oysters which have affixed themselves along with the other things which it is the 

 intention to destroy. The removal of the smaller forms from the surfsices of the slate would be 

 more difficult, and attended with danger to the fry already attached. With this object in view', 

 I would suggest the use of wooden" racks or frames lying horizontally, which would receive the 

 slates into deep notches made with a saw, so as to hold them vertically or edgewise, rendering 

 their removal, for the purposes of cleansing, and their replacement an easy matter. Other 

 devices would no doubt answer the same purpose and be more convenient even than the last. 

 If posts were securely fixed in the bottom eight, or ten feet apart, so as to project a foot or so 

 above the water at the highest tide, a single board six iuches wide, nailed against the tops of the 

 posts edgewise, and extending from one to the other, would provide a simple arrangement from 

 which to hang the slates singly by means of galvanized wire fastened or hooked to nails partly 

 driven into the board. By the help of this plan one man with a boat could overhaul many 



'E. INGEESOLL, Eeport on Oyster Industry, Tenth Census. 



