142 LABORATORY MANUAL FOR ELEMENTARY ZOOLOGY 



8. Section on embryology. The frog material used is preserved in formalin. 

 Excellent permanent mounts of halves of early frog embryos can be made as 

 follows: Use slides provided with cells, or make such a cell by sticking hard 

 rubber rings to the slide with balsam. Section the embryos with a sharp razor 

 and mount in the cell in glycerin jelly. The cover glass must be sealed with 

 cement or varnish. To make glycerin jelly, dissolve 6 grams of best gelatin 

 in 42 c.c. of water, and add 50 c.c. of glycerin, and 2 grams of carbolic acid 

 crystals. Warm (not above 75 C.), and stir until homogeneous. It must be 

 liquefied each time used by placing in warm water. 



9. Section on Mendel's law. Culture bottles for Drosophila are prepared as 

 follows: Use a wide-mouthed eight-ounce bottle stoppered with cotton. Put 

 a piece of very ripe banana in the bottle and sterilize. Stir up compressed yeast 

 with water to make a paste and drop 2 or 3 c.c. of this on the banana. Put also 

 into the bottle a piece of filter paper to absorb extra moisture. The female 

 flies to be used for a breeding experiment must be isolated from males within 

 a few hours after they emerge from the pupa in order to be certain that they are 

 virgin. The flies which we have been using originally came from the Depart- 

 ment of Zoology, Columbia University, New York, through the kindness of 

 Professor T. H. Morgan. 



10. Section on Protozoa. Cultures of Protozoa and other micro-organisms 

 may be prepared as follows : 



a) Gather a lot of aquatic plants, rotten lily pads, etc., from a pond, pack 

 into a vessel, add just enough water to cover them, and allow to decay. This 

 yields in about a month very good and lasting cultures of Paramecium, and 

 other Protozoa. 



b) Boil some wheat grains for a few minutes, and put into jars of water in the 

 proportions of about one to two dozen grains to two liters of water. Add a little 

 water, mud, or vegetation from a pond, or if desired to raise a pure culture add 

 a few individuals of the protozoan desired. 



c) Boil some hay in a quantity of water for several hours until the water 

 becomes dark brown. Put this brown water into jars with a small quantity 

 of the hay and inoculate with material from a pond or with the Protozoa desired. 



These three methods will yield all of the common Protozoa. Such cultures, 

 when they begin to die out, can be rejuvenated within two or three days by 

 adding some crumbs of stale bread. 



These methods, particularly the first, will commonly yield small amoebae, 

 but it is difficult to obtain a supply of large amoebae for a large class, and they 

 had better be purchased if possible. Old wheat cultures which have become 

 green often yield large amoebae, as do also cultures of diatoms. 



11. Section on Paramecium. To make Paramecium stand still, gelatin 

 solutions, jelly made from boiled quince seed, and jelly from Chondrus 

 (Irish moss) have been used satisfactorily by many people, particularly the 



