PRINCIPLES OF ANIMAL BIOLOGY 33 



going fission are found, note the position and depth of the constriction. 

 Look for contractile vacuoles. How many and where? If dividing 

 animals are found watch them at intervals until the process of division is 

 completed. 



In specimens stained and mounted on slides, observe carefully the 

 condition of the nuclei. Note that each paramecium has two nuclei, 

 a large macronucleus and a minute micronucleus. The micronucleus 

 in paramecia which are not undergoing division occurs in or near a little 

 hollow on the side or surface of the macronucleus. Look for it carefully. 

 In fission each of the two nuclei divides, a half going into each of the 

 daughter cells. Each daughter gets one of the old contractile vacuoles 

 and produces a new one. This type of reproduction is called binary 

 fission because each animal divides into two equal parts. Since division 

 is transverse it may also be called transverse fission in contrast to longi- 

 tudinal fission which occurs in some Protozoa. 



Make two drawings each two inches long showing an early and a late 

 stage of fission. Represent the body by an outline and make the nuclei 

 dark. 



2. Spore Formation. 



Spore formation in Monocystis. This is a protozoan parasite found 

 in the seminal vesicles of the earthworm. 



Examine a specimen in the cyst stage. The spindle-shaped bodies 

 are the spores, contained in the cyst. Estimate the number of spores 

 and record it in your notes. All of the spores have been produced by 

 the multiple division of a single cell. 



3. Budding. 



3a. Budding in the metazoon Hydra. Select hydras which bear buds 

 of various sizes, representing stages in the growth of these buds. Note 

 that the cavity of the bud is directly continuous with the cavity of the 

 parent. The bud is formed by the simple outpushing of both layers of 

 cells of the parent's body and the subsequent development of tentacles 

 and mouth. Tentacles are produced by a process similar to budding. 



Make an outline drawing of parent and bud. 



36. Budding in a metazoon, a fresh water sponge. The fresh water 

 sponges exhibit a sort of internal budding. As autumn approaches 

 certain cells in the body wall aggregate into spherical groups and become 

 surrounded by a protecting shell. These spherical bodies are called 

 gemmules. Examine a specimen containing them. In some species 

 several gemmules may be enclosed in a common envelope. The adult 

 sponges die in the autumn, but the gemmules live through the winter and 

 develop into new sponges in the spring. Crush a gemmule under a cover- 

 glass. Distinguish the whitish cells of the interior from the brownish 

 protective coat. Examine gemmules that have been boiled in caustic 



