19 

 PLATE X. 



FRESH- WATER POLYPE. 



GENERAL CHARACTERS 



FIGS. 1, 2. Foot or liydrorhiza (Gr. rJiiza, root) attached to some floating body. 

 Mouth at free end. 

 Tentacles or feelers (L. tentare, to feel) surrounding the mouth. 



( Testis, the male organ. 

 Reproductive organs j Oyary> the female orgM _ 



Multiplication by budding or gemmation (fig. 2). 

 GENERAL STRUCTURE 



DIAG. 1. Ectoderm (Gr. ektos, outside; derma, skin) (red). 

 Endoderm (Gr. endon, within). 



Body-cavity, serving also as a digestive cavity, and continued into the tentacles. 

 MINUTE STRUCTURE OR HISTOLOGY 



FIG. 3. Ectoderm-cells with contractile prolongations neuro-muscular cell-layer. 



Nuclei and nematocysts in the cells. 

 FIG. 4. Endoderm-cell with cilium on its inner surface. 

 FIGS. 5, 6. Thread-cells or nematocysts (Gr. nema, thread ; htsfos, a bag), consisting of capsule, 



filament, and three recurved spines at base of thread. 

 REPRODUCTION OR SEXUAL PROCESS 



FIG. 7, . Spermatozoon (Gr. sperma, seed ; zoon, an animal) with oval head and vibralile cilinm. 



b. Ripe ovum, consisting of vitellus or yolk, germinal vesicle or nucleus, and germinal spot or 



nucleolus. 

 e. Impregnated ovum divided into a number of cells, surrounded by a capsule burst to-show 



the contents. 

 MULTIPLICATION OR ASEXUAL PROCESS 



Process of gemmation shown in fig. 2. 

 DEVELOPMENT OF HYDROZOA 



DIAG. 2. The impregnated ovum by division becomes a mulberry-like mass or morula, the morula 

 becomes hollow by the accumulation of fluid in its interior, forming a planula, and the 

 planula by gradual thinning opens at one end, becoming the so-called gastrula, which 

 passes into the mature form. 



ffoie. In the Hydra itself there is no proper planula stage, as the two-layered form represented in c has no cilia. 

 CLASSIFICATION 



Sub-Kingdom Cffilenterata (Gr. koilos, hollow ; enteron, an intestine), because it is composed 

 of two cell-layers ectoderm and endoderm and has no cavity separate from the body- 

 cavity. 

 Natural Order Hydrozoa, because a digestive sac is not marked off from the body-cavity, and 



the reproductive organs are external. 

 Genus Hydra. 

 Common Name Fresh-water Polype (Gr. polus, many ; pous, a foot). 



THE EARTH-WORM. 



EXTERNAL CHARACTERS 



FIG. 1. The segmented body with a mouth at one end, an anus at the other, and a swollen portion called 



the ciugulum (L. a girdle) or clitellum (L. clitellee, a saddle). 

 FIG. 2. Mouth situated on the 2nd segment. 



External and internal pair of setae (L. seta, bristle). 



Openings of segmental organs, one on each side of all the segments except the two first. 



Openings of spermathe'cte or receptacles of the spermatozoa (Gr. ttperma, seed; thr.ke, a repository). 



Openings of vasa defcrentia (L. excretory ducts) on ventral face of loth segment. 



Openings of oviduct on ventral face of 14th segment. 



