376 REPORT—1863. 
position which receives confirmation from the fact that, even in those cases 
where they are most obvious, they become obliterated under slight pressure. 
At the summit of the sac 
the mesotheca is perforated 
by acircular aperture,round 
which its walls appear to be 
thickened, and probably con- 
tain here a rudimental cir- 
cular canal in which the 
radiating canals terminate ; 
at least, the presence of co- 
loured granules at this spot 
affords an indication of. the 
existence of such a canal. 
The ectotheca, which is 
loaded with thread-cells, is 
also perforated by an aper- 
ture corresponding to that 
of the mesotheca; and the 
gonophore is crowned by a 
circle of short tentacles (x), 
which seem to originate from 
the thickened margin of the 
perforation in the summit of 
the mesotheca, 
The tentacles possess, like 
the marginal tentacles of a 
true medusa, considerable 
contractility. They may 
frequently be seen of very 
different lengths in different 
gonophores of the same co- 
lony ; and this, which is 
really the result of different 
degrees of contraction, may 
be easily taken for different 
degrees of development, the 
tentacles being especially 
sluggi sh in the acts of Saat a, chitinous walls of the gonangium ; 3, blastostyle ; 
tension and contraction. ¢, opercular summit of blastostyle ; d, young gonophore 
Their length, when fully im the cavity of the gonangium; e, more mature go- 
extended in the female go- nophore, still in the cavity of the gonangium; /f, its 
nophore, will equal about tentacles turned back on the sides of the mesotheca ; 
: , meconidia; #, ectotheca, 7, mesothec: k, 
half the diameter of the etn ehiscn of meconidium ; J, radiating ae Fis ova 
gonophore: while under ex- become planule in the more mature meconidium ; 
ternal irritation, they will ~, tentacles of meconidium; 0, ciliated planula just 
slowly contract to a third of escaped from meconidium., 
their original length, and will then show themselves as a little stellate crown 
on the summit of the gonophore. They vary in number: I have counted in 
the female from 8 to 16 or 20. They are composed of ectoderm and endo- 
derm, the ectoderm containing thread-cells, and the endoderm presenting the 
usual septate appearance. They are less numerous and less developed in 
the male than in the female. 
Fig. 12.—Female gonangium with meconidia 
of Gonothyrea (Laomedea) Lovent. 
