
No. 426.] MADREPORARIAN CORALS. 471 
group are to be found specimens with from one to three or 
more oral apertures on a single disk. One may assume that 
all the individuals constituting a patch have arisen asexually 
from one or a few primary polyps. But such does not appear 
to be the case. Aggregations have been observed in which 
one large example would be surrounded by a number of others, 
all smaller but practically uniform in size. Both species are 
found to extrude larvae very freely, and there seems no doubt 
that the patches are in the main formed of individuals derived 
from such larvz as settled near the parent. A certain num- 
ber of fission polyps would also be expected. Externally it 
would be practically impossible to distinguish between larval 
polyps and fission polyps, but the internal mesenteries afford 
distinctive characters as to the one or the other form. 
Similar extensive patches of the large discosomid, Stoichactis 
helianthus (Ellis) are not infrequent. Their occurrence is 
probably to be explained in the same manner as above, that is, 
as due almost entirely to the aggregation of distinct larve. 
Asexual reproduction seems to be very rare in this species. 
Polyps of the northern species of Metridium usually occur 
in groups. From the researches of G. H. Parker! and others, 
asexual reproduction seems to play a considerable part in the 
crowding habit of these, but the possibility of aggregating 
larvae also should not be overlooked, even though M. margi- 
natum extrudes unfertilized eggs. 
JoHNs HOPKINS UNIVERSITY, 
BALTIMORE, Mp. 
l Parker, G. H. Longitudinal Fission in Metridium marginatum Milne- 
Edwards, Ju. Mus. Comp. Zoöl. Harvard, vol. xxxv, 1899. 
