782 
DR. E. B. WILSON ON THE DEVELOPMENT OF RENILLA. 
lature, so far as I am aware, is known to exist, though in most of the Actiniae the 
ectodermal muscles are very feebly developed, as Jourdan and the Brothers Hertwig 
have shown. This result can, however, hardly occasion surprise, in view of the 
astonishing amount of variation in the musculature of polyps. Kowalevsky states 
that the longitudinal muscles of Alcyonium are of entodermic origin, but refers 
the circular muscles doubtfully to the ectoderm. Beyond these, observations on the 
embryonic development of the muscles in Alcyonaria are wanting. 
In their mode of development the muscle-fibres agree with other Ccelenterata with 
exception of the Ctenophora. They are developed in the form of epithelio-muscular 
cells or myoblasts, which have the same form and structure as those of other Anthozoa, 
as described especially by the Brothers Hertwig and by Jourdan. The myoblasts 
do not, however, retain this form permanently, as is the case with many polyps. The 
cell-bodies become reduced to a small quantity of protoplasm enclosing a nucleus, and 
the myoblast is situated beneath the epithelial layer as in the medusae (Hertwigs), 
some hydroids (Korotneff, Ciamician), and a number of polyps (Hertwigs, 
Jourdan). It is, however, possible that some of the epithelio-muscular cells may 
retain this form permanently. 
III. 
DEVELOPMENT OF THE COLONY. 
The primary polyp of Renilla, produced by sexual reproduction from the egg, 
begins at a very early age to produce secondary polyps by budding, and thus builds 
up a community or colony of individuals organically united together. Although this 
process is a very common one among the Anthozoa, and is all but universal among the 
Alcyonaria, it possesses a special interest in the case of Renilla , on account of the very 
early period of life at which the power of asexual reproduction is developed, and 
more especially from the remarkably definite and constant structural relations existing 
between the members of the community. 
§ 14. Development and functions of the first pair of sexual polyps. 
When the larva is no more than seventy-two hours old, and is still actively swimming 
through the water, a pair of buds make their appearance on the dorsal side, just 
above the point where the dorsal and dorso-lateral septa join each other and the 
peduncular septum. This position of the buds is entirely constant, and I have never 
seen the least variation from it in the many hundreds of specimens examined. 
The buds, as shown at yd. in figs. 103, 104, appear as slight rounded elevations, with 
darker centres and without visible septa or mouth-openings. Upon making a longi¬ 
tudinal section through the bud at this stage (i.e., a section transverse to the axial 
polyp) we find that the darker centre is produced by an ingrowth of ectoderm 
