784 DR. E. B. WILSON ON THE DEVELOPMENT OF RENILLA. 
bottom. By the constant repetition of this process the whole organism moves slowly 
forwards. The creeping movements are very irregular, since the action of the muscles 
is not uniform. The longitudinal muscles frequently contract more on one side than 
on the other, so that the body sways and twists about from side to side, often turning 
completely over and undergoing all kinds of contortions. Nevertheless the organism 
often creeps for a considerable distance and may even crawl up the perpendicular sides 
of a glass vessel. The same power of active movement is possessed by the adult 
colony, and the conditions under which the organism lives are obviously such as to 
render this power of vital importance to the creature. Living as it does on shifting 
beds of sand, the colony would be buried and smothered were it not for this power of 
creeping. If, however, a Renilla colony be covered with sand in the aquarium, it soon 
works its way to the surface and the polyps are enabled to expand in the water. 
In the vital necessity of the power of movement lies no doubt the explanation of 
the very early appearance of the buds. If the young polyp, upon abandoning its free- 
swimming life and settling in the sand, possessed no means of taking in water and 
thus of creeping, it would be very apt to be smothered in the shifting sand. By the 
very early appearance of the buds the young polyp is enabled to imbibe water and to 
creep as soon as the sedentary life is assumed, and is thereby preserved from destruction. 
This view receives a strong confirmation upon comparing Leptogorgia with Renilla 
in this respect. The former does not possess the power of creeping but attaches itself 
at an early age to solid objects in situations where it is not likely to be buried. 
Precisely as we should expect under the foregoing view, the buds of Leptogoryia do 
not appear at an early period. In my specimens, in fact, they had not made their 
appearance at the end of nearly two months (!), whereas in Renilla they appear at 
the end of three days. 
As the buds become older and more fully developed they gradually cease to perform 
the function of imbibing water. It is however assumed by younger buds and is in 
turn lost by the latter as they become older. Throughout the entire life of the 
organism this function is performed by the sexual polyps in their early stages. The 
function is lost, so far as I have observed, as the bud becomes mature and is 
adapted to perform the functions of nutrition and reproduction, This may readily 
be demonstrated by placing a contracted colony in a vessel of water containing finely 
divided carmine. The water is forcibly sucked in through the mouths of all of the 
young marginal buds, but never through the adult polyps. This function is performed — 
by the zooids during their entire existence ; so that the latter structures are physio- 
logically identical with the young sexual polyps (see § 21). 
As may be seen in fig. 173, the bud lies at first almost entirely inside the primary 
polyp, projecting inwards from the body wall and forming only a very slight prominence 
on the exterior. As development proceeds the bud is pushed outwards so as to form 
an obtusely conical elevation on the exterior (fig. 178, p'.). At the same time the 
entoderm grows downwards from the tip of the bud in eight radiating plates (fig. 
