ANATOMY OF LIMNOCNIDA TANGANYICH. 283 
Examples of this invagination in a more or less modified 
form have been described and figured in many different genera 
of Hydroids, but in none does it exhibit quite sucha primitive 
condition as in Limnocnida. In the majority of Hydroids 
described, the invagination takes the form of an ingrowth of a 
solid mass of cells, called the “ glockenkern.” In some cases 
however, such as Hydractinia echinata, Weismann (15) 
Taf. xxiii, fig. 5, and better in the young buds of Clava 
squamata, Taf. v, Galeolaria aurantiaca, Taf. xxi, and 
Podocoryne carnea, Taf. xix, the “ glockenkern”’ is seen to 
be hollow in the youngest stages figured, but whether a cavity 
exists in any Hydroids from the first, or whether it is only sub- 
sequently formed as appears in the above cases, remains to be 
decided by future investigations. In Limnocnida the 
“glockenkern”’ is a hollow invagination from the very first, 
and its cavity becomes shut off from the exterior at a later 
period, but is typically retained throughout. 
The later stages of .Limnocnida buds, and especially the 
formation of the velum from two distinct layers of ectoderm 
which afterwards break through in the centre, are almost 
exactly paralleled by Bougainvillea fruticosa and Peri- 
gonimus cidaritis (Weismann, Taf. xii, figs. 10, 12, 
and 13). 
A noticeable feature in the development of the Medusa 
buds of Limnocnida is the entire absence of any trace of 
manubrium and mouth in any of the stages examined. It is 
true that in the adult the size of the manubrium is very insig- 
nificant as compared with the dimensions it assumes in other 
Meduse ; but nevertheless its entire absence in the young buds 
is, to say the least, remarkable. In the development of all 
other Medusa buds in the Hydrozoa, the manubrium is one of 
the most conspicuous parts of the young bud, and in the case 
of degenerate Medusz its presence is characteristic. The 
absence of manubrium and mouth in Limnocnida buds is, 
no doubt, to be accounted for by the fact that the young buds 
seem to obtain their nutriment direct from the gastric cavity 
of the pareut, and therefore have no need of a mouth or manu- 
