embryo always floats on top of the yolk, it may be readily observed with a hand 

 lens (or in later stages without such lens) by lifting ofT a piece of the shell. 



Watch for the first appearance of circulatory and nervous systems, and for 

 limbs. Note the distinguishable parts that become structures of the embryo or of 

 later stages; note what functions other parts of the egg serve. Make a summary 

 record of the development, with the help of drawings or photographs. 



3 To study the growth and development of houseflies, grow cultures under 

 observation in the laboratory.^ Note (a) what conditions favor the growth and 

 development of the species studied; (b) the number of offspring; (c) the character 

 and amount of parental care; (cI) the habits of the species that make them particu- 

 larly dangerous as carriers of disease or otherwise; (e) what methods suggest 

 themselves for their eradication. 



4 To make a study of the early development and metamorphosis of frogs, 

 toads or salamanders," watch the animals through the stages, in an aquarium. 

 Make careful notes and appropriate drawings showing the different stages in the 

 development. 



5 To find out how the snail develops, keep an egg-mass from an aquarium 

 in a small jar, where development can be traced in detail. (Snails require no 

 attention whatever if they are supplied with aquarium water containing a little 

 vegetation.) Examine the egg-mass regularly with a good hand lens or with a 

 microscope. Follow the development of the embryos. Describe the embryonic 

 development. 



6 To study the life history of a fish, observe the early and mature stages in a 

 fish hatchery. Find out how the eggs and sperms are obtained and used in the 

 artificial fertilization of fish; how the young are reared, and how they are trans- 

 ferred to streams and lakes. Describe the early development. 



7 To find out whether human proportions change between infancy and 

 adulthood, obtain several measurements of distance from foot to hip, hip to 

 shoulder, and shoulder to top of head, and plot the average measurements for each 

 dimension and for each age. Compare the separate curves as to slopes, which 

 indicate the relative rates of growth. Note which measurement changes the least 

 from infancy to maturity, and which the most. Find out whether there is any 

 period in development when growth takes place at an increased rate in all the 

 measurements. Summarize conclusions and interpretations. 



^To raise a generation of houseflies, place a pair of adult flies in a screened jar or cage 

 half filled with manure, or expose the jar for a day or two where there are flies. Use sufficient 

 manure to keep the mass moist, though not wet. 



-Collect eggs early in the spring from shallow pools along the borders of a pond or 

 stream. Supply green algae as food, and change the water frequently. 



365 



