566 REPORT—1863. 
The parallelism which I have thus endeavoured to demonstrate may be 
expressed in the following scheme. 
PHANEROCODONIC ADELOCODONIC 
| GonorHore. Gonoruore. Roum: 
Wetothectin 13; sayaie-asadededs -cseebinspases se dabzeee Ectotheca 
Wan bre lla ge ah wat re inadhanacuadeoake ade taante Mesotheca Basal web of tentacles 
in Laomedea flexu- 
osa, &e. 
Gastrovascular canals ..............scssececseees| Canals of mesotheca ./Base of tentacles ex- 
tending through the 
thickness of the 
body-walls. 
Ectoderm of manubrium ..................6.2. .[Endotheca .......++44. Ectoderm of probos- 
cis. 
Endoderm of manubrium ..................... (Spadix -tsusecasuehewse Endoderm of probos- 
cis. 
INVA GRIMALDI aia vinek vs oe'e sis. tris sav’ o0)s¥ «asain Spadix-+ endotheca.../Proboscis. 
Primary or radial marginal tentacula ...... Primary tentacula in Free portion of tenta- 
| the meconidium. cula. 
Secondary or interradial marginal tentacula Secondary tentacula| 
in the meconidium. 
Ocelli and TWthocysts.... 02. -..+.ccnersaeso sages ss 0 | 0 
MGlnMl avers sien stirtartacnceranis ancketeaecctatrice 0 0 
D. Further modifications of the gonosome. 
Besides the great leading differences already described, many others of a 
more subordinate kind are met with. The adelocodonic gonophore in parti- 
cular exhibits many special modifications, and presents us with a regular 
series of gradations in complexity, which throw much light on its morphology. 
The simplest form is probably that which we meet with in the female go- 
nophores of the freshwater Hydra. Here there would seem to be no differ- 
entiation of an ectotheca, while the spadix itself remains in a rudimental 
condition, being scarcely elevated above the base of the gonophore, whose 
whole cavity becomes at an early period occupied by the single large spheri- 
cal ovum. 
An advance over this condition is seen in the sexual bud which is borne by 
that form of medusa described above, under the name of “ gonoblastocheme.”’ 
Here we have the ultimate sexual bud quite destitute of ectotheca, and re- 
duced to the condition of spadix and endotheca separated from one another 
by the intervening generative elements (fig. 18, p. 401). 
In Clava, Hydractinia, &c., we have a still further advance in complexity. 
The gonophore has here the form of a simple closed sac, whose axis is occu- 
pied by a cylindrical or club-shaped spadix, round which the generative 
elements are clustered (fig. 6 A). Careful examination, however, will show 
that the walls of the sac consist of two membranes, an outer or ectotheca and 
an inner or endotheca. The mesotheca is entirely absent. 
In Garveia nutans, Wright, I have found a mesotheca to be distinctly de- 
monstrable ; but it is closed at the summit, and destitute of circular canal, 
while four short radiating canals may be seen in its walls extending from the 
base of the spadix for about a third of the height of the sac (fig. 6 B). 
In Tubularia indivisa the mesotheca presents the highest degree of deve- 
if the observer has correctly interpreted the appearances, the umbrella would be formed 
by the excayation of a solid spherical embryo. 
