122 FERTILIZATION AND EARLY DEVELOPMENT 



Exercise XXIII 



from the large batch onto a depression slide. 

 Examine under low power and count 30 to 50 

 eggs, classifying them according to cleavage 

 stage (the larger your sample, the more reliable 

 your results will be). For each succeeding count, 

 withdraw a fresh sample from the appropriate 

 batch of eggs. Tabulate your results when you 

 finish according to time (time from fertilization 

 to sampling) and cleavage stage (expressed as 

 per cent of total sample counted). Make a 

 graph showing the percentage of eggs uncleaved 

 and in each stage of cleavage as ordinate, against 

 the time as abscissa (use different colors for the 

 different cleavage stages). In such a graph, the 

 uncleaved eggs should form an S-shaped curve, 

 the various cleavage stages bell-shaped curves. 

 The peak of each of the latter curves represents 

 the characteristic time for that stage of develop- 

 ment. With these characteristic times, and 

 noting the temperature, prepare a schedule of 

 development for the species you have worked 

 with. 



MAMMALIAN SPERM 



Recently methods have been devised for 

 freezing and storing bull sperm for long periods 

 of time. Currently, artificial insemination, using 



sperm from a few superior bulls, is common 

 practice in the dairy industry. A suspension of 

 bull sperm will be available for examination. 

 Put a drop or two on a microscope slide, cover 

 with a cover slip, and observe immediately 

 under the compound microscope. Do not allow 

 the preparation to dry out. 



GENETICS EXPERIMENT 

 (continued: second week) 



During a lull, make the new matings in your 

 Drosophila experiment. The flies now in the 

 vials are the Fi generation. Etherize them care- 

 fully and examine them under the dissecting 

 microscope. Record the phenotype of every 

 fly. If they aren't as expected, consult an in- 

 structor; a mistake may have been made in the 

 original mating. 



Prepare two new sets of matings, placing 3 

 males and 3 females in each of two vials. Label 

 the vials, and store them in the boxes until next 

 week, when we will remove the parents. Two 

 weeks from today, the F2 generation will have 

 emerged, and the results of the experiment will 

 be analyzed. 



Why have no precautions been taken to ob- 

 tain virgin females for today's matings? 



EQUIPMENT 



Per student 



small petri dish 



2 droppers 



microscope slides and cover slips 



depression slide 



dissecting microscope 



compound microscope 



sea water 



prepared slides of sea urchin development 



diluted suspensions of sea urchin eggs and sperm* 



frozen bull spermf 



equipment for handling Drosophila is the same as 



for Exercise XXII 



2 vials for Drosopliila 



*Detailed instructions for setting up the sea urchin experiment will be found in E. B. Harvey's excellent 

 book, Tlie American Arbacia and Otlier Sea Urchins (Princeton University Press, 1956). Arbacia punctulata 

 is common on the East Coast, and Sirongylocentrotiis purpuratiis or S. franciscanus on the West Coast. The 

 latter forms, containing mature eggs and sperm, can be obtained during the fall and winter from the Pacific 

 Bio-Marine Supply Co., P. O. Box 285, Venice, Cal. 



fThis must be kept at dry-ice or liquid-nitrogen temperature. Deep freezers are not cold enough to main- 

 tain such preparations. Sources of bull sperm will be found in the yellow pages of telephone directories, 

 listed under "Livestock Breeders," or by contacting the county agent in agricultural communities, or any 

 agricultural college. 



