24 LABORATORY DIRECTIONS IN 



spherical bodies. How many cells do they contain? How are they held 

 together? Note that the cells on one side are larger than those on the 

 other side. The large cells are the reproductive or germ cells; the small 

 ones are sterile, and are called somatic (body) cells. How many kinds of 

 somatic cells are there? How many kinds of germ cells? 



Note if possible the slender whip-like structures projecting out from 

 each cell. These are the flagella, organs of locomotion. Do they pro- 

 ject beyond the jelly? Would movement of these flagella result in move- 

 ment of the individual cells, or of the whole group? Is the association 

 of the cells more close or less close than in the two preceding forms? 



Sketch Pleodorina. 



4. Volvox, like Pleodorina, is a free-swimming organism found in 

 fresh-water ponds. Study living specimens if available in a salt cellar 

 with the dissecting microscope. In case preserved material must be 

 used, place a few drops of liquid containing Volvox on a slide, add three 

 to ten grains of fine sand to support the cover-glass and then put on the 

 cover-glass. Compare with Pleodorina as to size, shape and number of 

 cells. 



Are the cells all alike? Note the numerous small cells of nearly uni- 

 form size. These are the somatic cells, held together by a gelatinous sub- 

 tance. In what part of Volvox are these cells located? Connecting the 

 somatic cells are slender strands of protoplasm. By counting in several 

 instances (not less than six) determine how many of these connecting 

 strands project from each cell. If living Volvox is available, focus on the 

 edge of a specimen, and fmd flagella projecting from each cell. Does the 

 beating of these flagella result in movement of the individual cells, or of 

 the whole organism? From the structure of Volvox, would you say 

 the cells are independent of each other? -*** 



Besides the small somatic cells, observe the larger bodies in Volvox. 

 These are either reproductive cells or daughter individuals derived from 

 them. Determine where they are located. The reproductive cells are 

 of three kinds: (a) parthenogonidia, which by cell division give rise to 

 daughter individuals asexually; (6) ova or eggs; and (c) spermatozoa (male 

 reproductive cells). 



4a. Parthenogonidia. Look for these in very small (young) individ- 

 uals. They are somewhat larger than the somatic cells and rarely as 

 many as a dozen in number. Some of them may be found to have divided 

 into two, four, eight or more cells forming small daughter individuals. 

 In older individuals look for daughters of various sizes. There may be 

 from four to nine of these. Eventually they break out of the parent. 



46. Ova may be 30 to 100 in number in certain species or as few as four 

 to eight in others. They are considerably larger than the somatic cells. 

 Find ova with spiny shells covering them. The shell indicates that they 

 have been " fertilized" by a spermatozoon and have gone into a resting 



