[17] ARTIFICIAL PROPAGATION OF OYSTERS. 757 



make a slight wave motion on the surface, the embryos will be seen de- 

 scending from that surface in long comet-like streams and tbese streams 

 invariably tend towards the sides of the glass. The mass of water will 

 present for several minutes a very peculiar, streaked appearance, due 

 to the descent of the embryos. Close observation will discover that 

 after reaching the bottom the embryos rise again through the water 

 (now quiescent) to the surface. If a shell is placed in the bottom of 

 the beaker the tendency of the streams to avoid the edges and pass 

 under the lower side is quite remarkable. Curious whirls and eddies 

 appear to exist, and it is noticeable how closely the embryos follow the 

 lead of the head of the column. 



Our observations at Beaufort showed us that after the embryos had 

 once developed the shell to any extent there was but little motion of 

 translation, the animals remaining quietly in one place at the bottom. 

 Indeed their specific gravity at this period, together with their defi- 

 cient locomotive powers, should prevent any very rapid or extensive 

 movements. Now it has been observed by numbers of persons, indeed 

 every one who has visited oyster regions, that the piles of wharves, the 

 trunks of trees near the water, the abutments of bridges and piers, and 

 many other substances similarly situated, are covered with young oysters 

 and sometimes with old, and that this attachment appears to be greatest 

 between the high and low water marks. ]S"umbers of floating objects 

 have also frequently been covered with the young fry, such as boards, 

 branches of trees, and the bottoms of vessels. Considering the fact that 

 the embryos swarm to the surface immediately upon the development of 

 their swimming i^owers, that upon any disturbance there they sink or 

 swim towards the bottom, making way diagonally as if in search of 

 some secure place for attachment, that as soon as shells are developed 

 they remain in a comparatively quiescent state at the bottom, and that 

 when it is possible large numbers attach about the surface of the water, 

 I have come to the conclusion that the oyster embryo is predisposed at 

 least to fix itself very soon after the process of segmentation is com- 

 pleted ; that as soon as cilia are developed they serve a double purpose, 

 not only affording a means of translation, but also one of fixation. This 

 is a hypothesis, of course, and the postulates upon which it is based 

 are onlj^ in a measure sound; but judging by the evident disposition 

 of the embryo with shell to remain at the bottom and nearly in one 

 place, I can account for the attachment at the surface of the water 

 only by assuming that it occurs at some period anterior to the devel- 

 opment of the shell. It is not very difficult to understand how the 

 embryos in swarms at the surface may be disturbed by a slight com- 

 motion of the waters, and streaming off obliquely to the bottom, may 

 come in contact, and be entangled by the cilia with any of the various 

 objects it is so frequently found attached to; and failing to find such, 

 it will continue its search until it reaches the bottom and then bury 

 itself under or about shells or other exposed " cultch." Failing to at- 

 tach there, it will rise again to the surface and repeat the process 



