The process carrying the otolith outer side of a or concretion hk, formed by endoderm cells, is tentacle, two enclosed by an upgrowth forming the " vesicle," nerves run round which is not yet quite closed in at the top. the base of the (After Hertwig.) tentacle to it.
The entocodon is to be regarded, therefore, not as primarily an ingrowth of ectoderm, but rather as an upgrowth of both bodylayers, in the form of a circular rim (IVa), representing the umbrellar margin; it is comparable to the bulging that forms the umbrella in the direct method of budding, but takes place before a manubrium is formed, and is greatly reduced in size, so as to become a little pit.
The blastopore, bl, has The extent of the shell and closed; the anus will subcommencing upgrowth of the sequently perforate the cormantle-skirt is indicated by responding area.
In the United States this artificial method has become a necessity, to prevent the upgrowth of alien communities, which might at some later date cause domestic trouble of a perilous character.