6 Invertebrate Zoology. 



several hours. Utilize the time while the piece is drying, by 

 drawing a cluster of the sponges (natural size, and also some- 

 what enlarged), illustrating such characters as have been 

 considered. 



Place the now dry piece of sponge upon a clean slide and 

 examine the cloacal surface, using a low-power objective. 

 The sponge appears to be made up of a multitude of needle- 

 like bodies or spicules. The spicules are clearly of two 

 kinds, radiate and linear. The radiate spicules form a some- 

 what regular lattice, each spicule producing its three longer 

 rays parallel to the wall of the cloacal chamber. A fourth 

 and shorter ray extends, from the common point of origin 

 of the three longer, perpendicularly into the cloacal chamber 

 and, as the sponge now lies, towards the eye of the observer, 

 as may be demonstrated by the use of the fine adjustment. 

 The linear or biradiate spicules are somewhat curved. Do 

 they lie in a plane mainly without or within the " quadri- 

 radiate spicules " ? 



Make drawings of the spicules, giving them their relative 

 dimensions. 



Remove the specimen from the stain, wash it for a 

 moment in water and then carry it through grades of alco- 

 hol to absolute. Clear in clove-oil and mount in balsam, 

 cloacal surface uppermost. (Do not allow the cover-glass 

 to rest too heavily upon the specimen.) Examine under 

 compound microscope. 



The spicules will now be found to lie below (outside of) 

 a layer of small cells, the endoderm, the nuclei of which are 

 clearly defined. The endoderm entirely covers the inner 

 surface of the cloacal chamber, and its cells, during life, are 

 provided with flagella and " collars" the activity of the for- 

 mer producing a current of water, which enters the chamber 



