another aquarium, as the mother fish may soon eat the young.) Compare this 

 method of reproduction in fish with that observed in most other fishes. Note the 

 probable mode of fertiUzation in these viviparous fish, 



8 To study the reproductive organs of frogs, dissect freshly killed male and 

 female frogs; locate, examine and describe the spermaries, sperm ducts, ovaries and 

 oviducts. Note the large size of the ovaries and oviducts. Count the eggs in a 

 portion of the ovary and estimate the total number in one female frog. From the 

 study of the internal organs describe reproduction in frogs. 



9 To find out how the fetus of a mammal develops within the uterus of the 

 female, dissect a pregnant guinea-pig, rat or rabbit late in the gestation period. 

 Note the stretched and enlarged uterus. Find the sac within which each fetus is 

 located. Note how the placentas are embedded in the uterine wall. Describe 

 mammalian reproduction. 



10 To investigate the reproduction of the hydra, examine living specimens 

 ander low magnification,^ identify buds in various stages and find individuals 

 with developed sex organs. Describe the methods by which hydras reproduce. 



11 To discover the reproductive organs of moss plants, use living male moss 

 plants which are distinguished by a cup-shaped tip, female moss plants, and female 

 moss plants with sporophytes attached. Place the tip of a male plant in a drop of 

 water on a slide, and with a stirring motion of a dissecting needle tease out the 

 antheridia (club-shaped organs bearing sperms). Remove the scales from the tip 

 of a female plant and then dissect out the archegonia on a slide with a needle. 

 Examine the base of a sporophyte and its attachment to the tip of the female, or 

 mother, plant. Examine spores from the capsule at the end of a stalk. Crush a 

 sport capsule over the surface of a dish of diluted Knop's solution' and set aside 

 for the growth of new individuals. Describe and illustrate methods of reproduc- 

 tion in mosses. 



12 To study reproduction in ferns, grow prothallia from fern spores and 

 observe microscopically from eight to ten weeks later.^ 



While prothallia are developing, examine under surfaces of leaves for the sori, 

 or clusters of sporangia. Crush sporangia on a sHde and examine them and dis- 

 charged spores with microscope. 



Look for antheridia and archegonia on under surfaces of fern prothallia (arche- 

 gonia just behind the notch; antheridia farther back). Mount prothallium on slide 

 and look for sperms swimming in the water. 



^Hydras can frequently be found on the sides of aquariums set up months earlier with 

 plants, snails, insects, and pond water collected locally. Cultures of living hydras can be pro- 

 cured from biological supply houses. 



^Knop's solution consists of 1 g each of potassium nitrate, magnesium sulfate, and potas- 

 sium phosphate, and 3 g of calcium nitrate dissolved in 1 liter of distilled water. Dilute to 

 ■^ strength to grow protonemata of moss. 



^Collect mature leaves of polypody, shield, or Christmas fern, with sporangia; dry in 

 dustproof boxes for a few days. Fill a thoroughly cleaned 3-inch or 4-inch flowerpot with 

 sphagnum moss or wet toweling; invert in a wet tray and dust fern spores on it; cover outfit 

 with inverted battery jar. Place culture in a cool place under moderate light. Water with 

 diluted Knop's solution. Germination should occur in a few days, and prothallia should 

 mature in from eight to ten weeks. 



396 



