212 ORIGIN OF SEX AND OF THE SOMA 



PRACTICAL WORK.' 



(i) In a sample of Chlamydomonas note,_under the low .power, 

 the moving green dots. Under the high power note in a specimen 

 at rest {the flagella often get stuck to the slide or coverslip, 

 and the cell thus anchored oscillates to and fro) the cell wall, 

 the basin shaped chloroplast with pyrenoid, the clear front end 

 of the body with the base of the flagella, and the red eyespot. 

 Look out for stages of division. Run a drop of dilute iodine 

 solution under the coverslip and observe again. 



(2) In a living demonstration specimen under aii apochro- 

 matic immersion lens' observe the finer detaUs of cell structure, 

 including the nucleus situated in the colourless central protoplasm 

 in the hollow of the chloroplast. 



(3) Examine if possible Pandorina and Eudorina (preserved 

 material if fresh cannot be obtained), noting the construction of 

 the ccenobium and the fact that the structure of each cell is 

 of the Chlamydomonas type. Examine also stages of division 

 to form daughter coenobia if these are available. 



(4) Volvox. In V. aureus (on the whole the commonest 

 species) note the large spherical coenobia, each consisting of 

 several hundred spherical cells. Compare several specimens, 

 and- trace the development of the daughter coenobia from the 

 large cells (parthenogonidia) of the mother. If sexual colonies 

 are available note the development of the sperms by repeated 

 division of special cells (androgonidia) and the large gynogonidia, 

 each of which becomes an egg. 



(5) Examine a single vegetative cell under the high power 

 and note that it is of the Chlamydomonas type. Look for the 

 flageUa. Run in a drop of iodine and look for the threads of 

 cytoplasm connecting the cells. 



(6) Compare the structure of V. globator, and examine any 

 demonstration slides of stages of development and details of 

 cell structure that may be available. 



' The material for this practical work may be varied according 

 to what can be obtained. Chlamydomonas is generally available 

 during the warmer months, and can in any case be kept in the labora- 

 tory without much difficulty. The coenobiate forms are not so easy 

 to keep in cultivation, and fresh material is by no. means always 

 available. For this reason it is advisable to keep a stock of material 

 preserved in formalin, illustrating at least the vegetative structure 

 of Pandorina, Eudorina, Pleodorina, and Volvox, and the formation 

 of daughter coenobia in these forms. Pleodorina can often be found 

 by careful searching through samples of Eudorina. It is desirable 

 also to prepare slides showing the formation of gametes, etc. 



