40 PORIFERA 



stage (see figures in the textbooks). They then break 

 through the choanocyte layer into the radial canals and pass 

 out with the current of water. Living specimens are fre- 

 quently found with such embryos issuing from the oscula in 

 the outgoing current of water. The sperm spheres, when fully 

 developed, also break through the choanocyte layer and, 

 separating into their component spermatozoa, pass out with 

 the outgoing water. 



Ova and sperm are formed by the same individual, and 

 the animal is therefore hermaphroditic, but the products 

 ripen at different periods and are seldom both present in an 

 individual at the same time. 



If the time allows, draw ova, sperm spheres, segmenting 

 eggs, and embryos. 



It is desirable to examine specimens of Leucosolenia, a 

 still simpler sponge, and of some of the more complicated 

 forms, like commercial sponges, Spongilla, Cliona, and 

 Chalina. Why is more than a single osculum desirable in 

 such forms? Understand the relation of the internal struc- 

 ture of the complicated forms to the more simple forms. 

 What reason is there for the complication? 



The individual cells of sponges (Microciona) may be 

 separated by squeezing through fine silk bolting cloth. Such 

 cells will come together in a dish of sea water to form ag- 

 gregates that will develop into new sponges. (See Wilson 

 and Galtsoff, loc. cit.) 



