2. Sexual reproduction : hydra is monoecious (hermaphroditic), 

 the same animal producing eggs and spermatozoa. 



(a) The spermaries are swellings of the body wall produced by 

 the local multiplication of interstitial cells, and covered on the 

 outside by a cap formed of large ectodermal cells. The spermaries 

 are situated just below the tentacles. How many do you find? Is 

 the number constant? Find a ripe spermary and observe the move- 

 ment of the spermatozoa within the capsule. By gentle pressure 

 upon the cover glass break open the capsule and observe the swim- 

 ming of the spermatozoa and their size and shape. 



(b). The ovaries usually develop later than the spermaries and 

 are formed near to the base of the animal. How many do you find? 

 Is the number the same in the brown and green species ? Single 

 cells of each ovary enlarge to form the ovum, while the other cells 

 nourish it and form a capsule about it. 



Make drawings of buds and of the sc.rual organs. 



IV. STUDY OF PREPARED SECTIONS. 



Examine series of transverse and longitudinal sections of hydra 

 prepared by the paraffin method, and note the large central enteron 

 surrounded by a body wall of two layers of cells. 



1. The ectoderm. Is it of uniform thickness? In it observe: 

 (a) Large squarish or conical cells. Do they contain nuclei and 

 vacuoles ? Their basal ends are continued into muscle fibres 

 (Klinenberg's Fibres) which are mainly longitudinal in direction, 

 and in cross-section appear as a row of refractive dots on the sur- 

 face of the supporting lamella. Over the outer surface of these 

 cells is a thin cuticle. At the foot the ectoderm cells are more 

 columnar and contain granules, (b) Interstitial cells are present over 

 the body and tentacles but absent in the foot ; they stain deeply, 

 (c) Nematocysts, abundant in the tentacles, less numerous on the 

 body and absent on the foot. Are they found in the endoderm? 



2. The supporting lamella. A thin, deeply staining layer be- 

 tween the ectoderm and the endoderm. Is it composed of cells? 



3. The endoderm cells ; variable in shape and size. They are 

 of two kinds: (a) Larger cells, irregular in shape and size, con- 

 taining A^acuoles, and with the nucleus flattened and near the basal 

 end. In H. viridis the basal part of each cell contains rounded 

 bodies, chloroplastids, coated with chlorophyll. In H. fusca similar 

 bodies are present, "sooty corpuscles", devoid of chlorophyll. The 

 basal ends of these cells are often prolonged into muscular processes 

 like those of the ectoderm cells, but transverse in direction, (b) The 



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