102 
CHARLES L. BOULENGER. 
the radial canals prove to be nothing more than the hollow 
bases of the tentacles which have grown out centifugally from 
the stomach in much the same way as the accessory radial 
canals of Aequo rea have been known to do. 
This theory would thus explain the independent origin of 
the four radial pouches from the endoderm of the young 
medusa-buds. 
The development of the buds of Limnocnida throws 
considerable light on the difficult problem of the relationship 
between the medusoid and liydroid individuals in the 
Hydromedusae ; I heartily agree with Hadzi in considering 
these forms as strictly homologous structures, but can see no 
necessity for abandoning Weismann ; s old-established theories 
on this subject. 
There can be no doubt that Gunther was right in con- 
sidering that in Limnocnida the formation of the entocodon 
by invagination is a primitive feature, and that the solid 
ingrowth of ectoderm which occurs in the young buds of the 
majority of the Hydromedusas merely represents a modifica- 
tion of such a process of invagination. 
In my opinion the formation of a two-layered cup of 
endoderm is another primitive feature in the development of 
Limnocnida; even in this genus it persists only for a very 
short time and almost simultaneously with its formation 
becomes constricted at the interradii to form the endoderm 
lamella, leaving four distinct and comparatively large 
perradial pouches, which are obviously homologous with those 
of other medusa-buds. 
In the development of all types of gonopliores in the 
Hydromedusae we meet with a considerable shortening of 
their ontogeny, and it seems to me that where, as in the 
majority of forms, the four radial pouches arise independently 
from the endodermal cavity of the young bud we are dealing 
with a process of this nature, and that the primitive two- 
lavered cup stage has been suppressed. 
If this argument be accepted we can still retain Weismann’s 
views on the phylogeny of the medusoid individual, in spite 
