242 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
tion. The circular outline of the disk is soon lost, the little sponge spreading in an 
irregular fashion over the surface to which it is now firmly attached. In two or three 
days the metamorphosis is complete, and we have a sponge, very small, to be sure, 
and without reproductive elements, but like the adult in fundamental structure. Its 
surface is perforated by minute apertures, the pores, through which water enters the 
body, and by a few larger apertures, the oscula, through which the water leaves the 
body. Ramifying through the interior is a system of spaces or cauals which connect 
the pores with the oscula. Portions of this canal system form small spheroidal 
chambers, the walls of which are studded with cilia. It is owing to the motion of 
these internal unseen cilia that a current of water is constantly circulating through 
the sponge body, carrying to its tissues the oxygen aud food (minute particles of 
animal and vegetable organisms) necessary for their life. 
How long it takes for a sponge developed in this way to reach adult size and 
begin breeding is unknown. I have kept young sponges that have transformed 
aud attached to the walls of my laboratory aquaria for days and weeks. After the 
first few days the increase in size has generally been imperceptible. But the unfavor- 
able conditions incidental to such an unnatural habitat were doubtless responsible for 
this lack of success. 
PRACTICAL SUGGESTIONS ON REARING SPONGES. 
More species of sponges breed during the warm season than at other times. Yet 
in the Mediterranean (Naples) some sponges are found breeding at all times of the 
year. In the Bahama Islands and on our own coast, I have found the breeding time 
of many sponges to fall within the period from midsummer on through early autumn. 
For the inauguration of experiments I should recommend the months of July, August, 
and September. 
It is easy to determine when one of the horny or silicious sponges is breeding. 
On cutting out a piece of the sponge, the developing eggs scattered through the 
tissues can be seen without the help of a lens. They are minute, rounded bodies, 
often very uutnerous, and sufficiently conspicuous to catch an observant eye. 
The means employed for getting young sponges must always be different from 
those made use of in the case of animals like fish, oysters, etc., in which artificial 
fertilization is practicable. Since the sponge egg is fertilized and undergoes its early 
development in the body of the mother, artificial fertilization is here of course out of 
the question. 
The young in numbers ample for study can, however, be obtained in the following 
easy manner. The sponge being raised to near the surface of the water is then 
dipped up in a glass aquarium or bucket, in such a way as not to expose the animal 
to the air. In a few minutes time the ciliated larvae will begin to be discharged. In 
the study of some Bahama sponges I found it convenient to take to the sponge- 
grounds, in a boat, a couple of good-sized tubs. In one of these some sponges would 
be placed for about half an hour. At the end of that time they were transferred to 
the second tub. The water of the first tub was meanwhile examined for the sponge 
larvae. In this I was aided by negro boys, who soon became expert. We bailed out 
the water in 2-gallon glass vessels in which the little larvae could readily be seen. 
The latter were then picked out with glass tubes and placed in a special dish. By the 
time the examination of the first tub was completed, the second would be found to 
