456 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
ment. Within the last few vears, however, a number of observers- 
t/ J ' 
have discovered this phenomenon in the developmental stages of vari¬ 
ous forms. 
Attachment. 
Under favorable conditions when the larva is about fifty hours old 
it reaches that stage of development at which attachment takes place. 
In preparation for this process the planula settles to the bottom, 
loses its cilia, and consecpiently its movements cease. The manner 
of attachment in Turritopsis like that in Stomotoca differs from that 
usually described in hydroid development. Instead of settling down 
on the anterior end of the planula according to the method which 
occurs in Eudendrium, and which has been regarded as typical and 
used in descriptions of the embryology of the hydromedusae in text¬ 
books, the planula becomes attached on its side by nearly its whole 
length and is transformed into a root. The hydranth instead of 
growing up from the posterior end of the planula as in forms which 
attach themselves by- the anterior end, develops from a bud that is 
given off from the root, usually at about the middle. 
Professor Brooks observed the fact that the planula is transformed 
into a root in Turritopsis, Eutima, and Hydractinia, and gives a brief 
account of the same in his paper on “The life history of Eutima’’ 
(Brooks, ’ 84 ). Metschnikoff (’ 86 ) describes and figures for Mitro- 
coma the fact that the larva becomes attached by its side and is almost 
wholly employed in the formation of the hydrorhiza, while the first 
hydranth grows out of it by a kind of budding. 
In general the attachment of the planula is similar in Turritopsis 
to the method which is followed by Stomotoca, but the former does 
not commonly produce secondary hydrorhiza. In Stomotoca at about 
the time the hydranth bud appears, or even before, the root branches, 
giving rise usually to one or two secondary roots. In Turritopsis 
this branching rarely takes place, at least during the first few days 
of the development of the hydranth. 
Professor Brooks describes and figures in the planula of Eutima an 
ectodermal adhesive gland. It occurs after the endoderm and the 
digestive cavity are formed, and before the appearance of the mouth 
as an ectodermal invagination at the small end of the planula. In 
Turritopsis no such special organ of attachment is found. The larva 
