OTHER SPONGES 85 



recognized; refer to figures in textbook and Fig. 41. The beating of 

 the flagolla upon the choanocytes brings about the current of water 

 through the sponge. Look for the prosopyles leading from incurrent 

 to excurrent canals. In the gelatinous ground substance between the 

 dermal and gastral layers are found several other cell types: large 

 amoeboid cells, the archaeocytes, which are capable of amaboid move- 

 ment; scleroblasts, which secrete the spicules; collencytes, or connec- 

 tive tissue cells ; early germ cells, which resemble archseocytes ; masses 

 of spermatozoa; and fully developed ova. Sponges are commonly her- 

 maphroditic, but the ova and spermatozoa may be produced at differ- 

 ent times in the same individual. Fertilization occurs and the zygotes 

 develop within the region between the two cell layers; ciliated larvae 

 are formed which leave the parent sponge by way of the excurrent 

 canals, cloaca, and osculum. Draw (3-5 X projected size), showing 

 the cellular organization as observed in the preparation you have 

 studied. 



(e) The spicules can be examined in thin sections of a dried 

 grantia in temporary or permanent mounting. Observe their arrange- 

 ment in the section and note the different kinds. Also examine the 

 spicules as they appear in a drop of the residue obtained by boiling 

 a Scypha in a solution of sodium hydroxide. Draw (3-5 X projected 

 size), showing arrangement of spicules to constitute the skeleton of 

 the normal sponge. 



OTHER SPONGES 



Exercise 1. — ^Various Species. 



(a) Stained sections of the sponge Leucosolenia, and pieces of the 

 wall mounted whole, may be studied to illustrate the organization of 

 a sponge having the ascon type of canal system (c/. Fig. 41). 



(b) Examine: dried specimens of glass sponges, in which the 

 skeleton is composed of siliceous spicules; and specimens of horny 

 sponges, such as the bath sponge, Euspongia. The canal systems 

 of the larger and more complex sponges may be compared with that 

 of grantia as shown by Fig. 41. 



(c) The fresh-water sponges, Spongilla and Ephydatia, are found 

 in clear ponds and streams attached to stones or other submerged 

 objects. They are easily collected but difficult to maintain in the 

 laboratory. Actively growing specimens occur during the warmer 

 months, but in winter only granular encrustations composed of gem- 

 mules which develop into new colonies the following spring. 



