On the Contractile Substance of the Polythalamia. 351 
Perithecia forte interdum subtus (exoperithecio) subincoloria, 
et spore ad faciem stirpis Verrucarie epidermidis vergentes. 
Paraphyses nulle rite evolute, nec filamenta ostiolaria ulla visi- 
bilia (D. Fuisting ea dixit “periphyses;” melius dicerentur 
anaphyses, si nomine novo egeant). Apothecium latit. circiter 
0-1 millim. 
XL.—On the Morphological Structure and the Motory Phenomena 
of the Contractile Substance of the Polythalamia (Gromia ovi- 
formis)*. By M. ReicHerr. 
1. In the Polythalamia two substances are distinguishable, in- 
dependently of the shell: the contractile substance of the body, 
and the colourless constituent which forms the central mass of 
the body and contains colourless and coloured corpuscles as well 
as vesicles. 
2. Nothing has been accurately determined in regard to the 
morphological composition of the central substance of the body 
containing the vesicles, in Gromia oviformis. Vesicular bodies 
of the size and structure described by M. Schultze, ‘ Ueber den 
Organismus der Polythalamien,’ &c. p. 21, and figured in pl. 1. 
fig. 6, pl. 7. figs. 10 and 12, were not observed. Whether the 
apparent vacuoles of the contractile cortical substance, which are 
not described by this observer, led to the idea of the existence 
of vesicular bodies, or whether I have not been so fortunate as 
to obtain animals with true vesicles situated in the central sub- 
stance of the body, future observations must decide. 
3. The contractile substance of the body forms the cortical 
layer of the soft body of the Polythalamia, which surrounds the 
central substance containing the vesicles. Whether this was 
provided at the mouth of the shell with an orifice could not be 
ascertained in Gromia oviformis; but in one instance a granular 
flocculent mass, probably arising from the central substance, was 
observed at the orifice of the shell. The contractile substance 
of the body in Gromia oviformis forms a depressed ellipsoidal 
hollow sac corresponding in external form to that of the entire 
body, and hence accommodates itself, as in other Polythalamia, 
to the shell, with the necessary regard to the siphons. It pro- 
bably takes part in the formation of the shell, but appears sub- 
sequently to separate almost entirely from it, as the sea-water 
enters between the shell and the cortical substance even at its 
wide commencement ; it is also well known that the soft body of 
Gromia oviformis partly leaves the shell. Besides contractility, 
* Translated by J. W. Griffith, M.D., F.L.S., from the ‘Monatsbericht ’ 
of the Berlin Academy, Aug. 1865, 
