86 LABORATORY MANUAL FOR ELEMENTARY ZOOLOGY 



Draw a small portion of the section in great detail to show all the kinds of 

 cells present. 



6. Reproduction. Hydra reproduces by the asexual process of budding or 

 by the reproduction of eggs and sperm in definite reproductive organs. Living 

 material with sex organs is available only in the autumn. 



a) Budding: If living specimens with buds are available obtain one and 

 make a simple outline drawing. 



b) Male reproductive organs: Examine slide at demonstration microscope. 

 The male organs, spermaries or testes, form conical elevations in the ectoderm 

 each provided with a nipple-like extension for the exit of the sperm. Draw. 



c) Female reproductive organs: Demonstration slide. The ovaries are located 

 nearer the aboral end than the testes, form low broad elevations, and lack the 

 nipple. Each contains a single (or sometimes two) large amoeboid ovum. Draw. 



7. General considerations on Hydra. The chief differences that we may 

 note between Hydra and the Protozoa is that it consists of several different kinds 

 of cells, each with specific functions, and that these cells are arranged in definite 

 layers, which foreshadow the systems and organs of the higher animals. To 

 what stage of the embryonic development of the frog does the Hydra correspond? 

 Which of its two layers is the more differentiated and what reason can you give 

 for this? In Hydra, digestive, muscular, reproductive, and nervous (see Hegner, 

 p. 125) systems are present, at least in a simple condition. What systems 

 which the frog has are totally lacking in the Hydra and how does it accomplish 

 the functions performed by those systems when they are present? In what 

 way is the process of digestion in Hydra like that of the frog and in what way 

 like that of the Protozoa (Hegner, p. 127)? 



We may further notice that the Hydra is not merely a collection of many 

 cells of several different kinds but that these cells act together for the general 

 welfare of the animal, and each one is more or less helpless without the others, 

 since it has become specialized for particular functions, and hence cannot success- 

 fully perform all functions like a protozoan cell. Hydra is therefore an individual, 

 a unity produced by co-operation, ruled by a dominant region, the anterior end 

 or head, which, to be sure, is as yet not very distinctly differentiated from the 

 rest of the body. 



B. A COLONIAL COELENTERATE 



For this study either Obelia or Campanularia may be used. As these animals 

 live in the ocean, only preserved material can be obtained. Obtain a preserved 

 colony and examine in a watch glass of water (Hegner, pp. 139-40). 



i. General structure. The coelenterate forms a branching colony of plant- 

 like appearance consisting of a number of individuals, each of which is similar 

 to a Hydra. Identify the rootlike basal branches, the hydrorhiza, by means of 



