GENERAL BIOLOGY 



These various organs and systems will be considered in detail 

 in connection with each of the animals studied. 



DEVELOPMENT OF OVUM 



In prepared slides of Echinoderm eggs observe the following 

 stages: i. Cleavage; i-cell, 2-cells, 4-cells, 8-cells, i6-cells, 32- or 

 64-cells. Observe the appearance of a cleavage cavity after the 

 8-cell stage. 



2. Blastula: Observe the hollow sphere composed of a single 

 layer of cells (Epithelium). Are there any indications that scat- 

 tered cells (Mesenchyme) migrate into the cavity of the blastula 

 (Blastocoel) ? 



3. Gastrula: Note the flattening and ultimate infolding of the 

 blastula at one pole. Do the cells at this pole differ in appearance 

 from the others? The infolded cells constitute the endoderm, the 

 outer layer the ectoderm. The infolded cavity is the Gastrocoel, or 

 digestive cavity; the opening to the exterior is the Blastopore. 



Draw and label the stages and structures named above. 



HYDRA VIRIDIS OR FUSCA, Freshwater Hydra. 

 (Phylum Cnidaria, Class Hydrozoa.) 



Read: Calkins, Biology, pp. 76-102; or 



Parker, Elementary Biology, pp. 221-236; or 

 Parker and Parker, Practical Zoology, pp. 2&g-3i4', or 

 Woodruff, Foundations of Biology pp. 118-121. 



A Metazoan which throughout life remains in a two layered con- 

 dition, like a gastrula. Observe with naked eye, or with pocket 

 lens, the hydras in a jar of water where they have been undisturbed 

 for some time. Notice the general habitus of body, method of 

 obtaining food, etc. Transfer a hydra to a slide with plenty of 

 water, and observe with the dissecting microscope ; afterward 

 cover, supporting the cover glass so as not to crush the animal, 

 and examine wtih the low power of the compound microscope. 



I. FORM. 



The body: What is the general shape? Do its length and 

 breadth vary? It is usually attached at one end, the foot, by a 

 kind of sucking disk and terminates at the other in a conical pro- 

 jection, the hypostome, with the mouth at its summit. The mouth 

 is a small aperture, but it can be greatly dilated to take in food. It 

 opens into a central digestive cavity, the enteron. The tentacles 



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