The spermatogenesis of Hydra. 425 
Explanation of plates. 
Plate 29! 
Fig. 1. The earliest figure of Hydra with testes, after BAKER, 1743. 
Fig. 2. Section at margin of a spermary (HH. fusca); shows multipli- 
eation of the primordial germ cells. 1342:1. 
Fig. 3. An ectoderm cell. 1342:1. 
Fig. 4 An ectoderm cell dividing amitotically. 1342: 1. 
Fig. 5. Section through a mature spermary, showing general ar- 
rangement of the generations of cells during spermatogenesis. 580 : 1. 
Plate 23. 
Fig. 6. Female of H. dioecia. 22:1. 
Be. 1. Male of 7 dioecia.! 22:1. 
Fig. 8. FH. viridis with mature ovary and testes just appearing. 
mas). 
Fig. 9. Section of H. dioecia taken through spermary to show 
elongated ectoderm cells. 415: 1. 
Fig. 10. H. dioecia, male, copied from BRAUER. 
Fig. 11. Cross section of H. dioeria, through spermary, to show 
relative proportions of parts. 220: 1. 
Fig. 12. Section through ectoderm of H. dioecia; a primordial 
germ cell dividing, 1342: 1. 
Fig. 13. Section at base of spermary (H. fusca); endoderm cells 
vacuolate, but elaborating nutritive material for the spermatogonia, 1342:1. 
Fig. 14. Section of H. dioecia; a budding individual. 1342:1. 
Plate 24. 
Fig. 15. Section of H. dioecia; early stage of spermary. 1342:1. 
Interstitial cells in early prophase of mitosis. 
