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 canals 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 and 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 

 and 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 numerous, 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 



