142 Papers from the Department of Marine Biology. 
In Asterina (Bury, 1), while the anterior enteroccele is essentially a 
double structure, there are three communications between them—a 
ventral just below the hydroccele and two dorsal, one just above the 
hydroceele and a second behind the pore. In Laganum, although the 
body of the embryo is compressed dorso-ventrally and the lumen of 
the cavity in that region is consequently very narrow, there seems 
to be no separation of the right and left portions into distinct lobes. 
BILATERAL SYMMETRY. 
It is evident that in Laganum there exists a bilateral symmetry not 
characteristic of other forms of echinoderm larve at a corresponding 
stage of development. The cavities of the anterior enteroccele at 
each side of the gut are usually of about equal size and extend approxi- 
mately the same distance towards the posterior end. The ring of the 
hydroceele lies immediately in front of the centrally located gut, and 
its lobes have a perfect bilateral symmetry with regard to the median 
plane of the animal. On each side of the posterior primary tentacle lies 
one of the vesicles which together represent the posterior enteroccele. 
The only interruption of the bilateral symmetry is caused by the pore 
canal which, arising from the left side of the hydroceele ring and circling 
around the gut, opens to the exterior, well to the left side of the pluteus. 
Whether this symmetry, which has not been described for so late a 
stage of the echinoderm, is a primary or a secondary development 
could of course be definitely determined only by a study of earlier 
stages. But, however this condition arises, it is evident that we have 
here a form unusual not only in regard to this characteristic, but also 
in respect to other fundamental properties, such as the rapidity of early 
growth, the great complexity of the larval skeleton, the formation of 
the amniotic cavity from a central invagination, the entire absence of 
right posterior enteroccele and hydroccele, and the complete constriction 
of the left posterior enteroccele into two separate vesicles. 
Bryn Mawr Co..ece, January 8, 1915. 
BIBLIOGRAPHY. 
. Bury, H. Studiesin the embryology of echinoderms. Quart. Journ. Micr. Sci., vol. 29. 1889. 
. Goto, S. The metamorphosis of echinoderms, with special reference to the fate of the body 
cavities. Journ. Coll. Soc. Imp. Univ., Tokyo, vol. x. 
. MacBripg, E. W. The development of Echinus esculentus. Phil. Trans. Roy. Soc., vol. 
cxcv. 1903. 
. MacBripgz, E. W. The development of Echinocardium cordatum. Quart. Journ. Mier. Sci., 
vol. 59, N.S., No. 236. 1914. 
. Peace, L.M. Clearing and staining leaves and stems. Plant World, vol. 13, No.4. Apr., 1910. 
. TENNENT, D.H. Echinoderm hybridization. Carnegie Inst. Wash. Pub. No. 132. Jan. 1911. 
. Taher, H. On the development of Echinocyamus pusillus. Nova Acta. R. Soc. Sci., 
Upsala. 1892. 
Noe 
ISO thee w 
