1886.] 



MICROSCOPICAL JOURNAL. 



228 



The body of Uvdra is resolvable 

 into two distinct layers, an inner — 

 the endoderm — and an outer — the ec- 

 toderm. The 

 tentacles are 

 mere tubular 

 prolongati o n s 

 of these mem- 

 branes. The en- 

 doderm (fig- 

 19) consists of 

 a single layer of 

 large nucleated 

 cells of proto- 

 plasm, destitute 

 of an investing 

 membrane, but 

 enclosing, in 

 many cases, a 

 vacuole filled 

 with clear fluid. 

 According to 

 Kleinenberg a 

 few isolated 

 cells of the en- 

 doderm are fur- 

 nished with one 



or more very delicate cilia. Later 

 observers have asserted that the en- 

 tire endodermal layer is ciliated, and 

 it is further stated that strong amoe- 

 boid movements are shown by the 

 cells of the endoderm, more es- 

 pecially in those lining the body 

 cavity. The important fact is now 

 considered well established by re- 

 cent investigations of T. J. Parker 

 and others, that the digestion of the 

 solid food particles swallowed by 

 fm Hydra takes place in the protoplasm 

 of these endodermal cells, the latter 

 acting almost exactly like an aggre- 

 gation of amoebcB. In the endodermal 



cells of U. viridis are also imbedded 

 the green granules which give to that 

 species its distinctive color. Their 



Hydra Viridis. 



function is not definitely known. It 

 is an interesting feet that, after the 

 most searching investigation of their 

 optical and chemical properties by 

 Kleinenberg, Cohn, and others, it has 

 been made a matter of the strongest 

 probability that these green corpus- 

 cles are identical with the chloro23hvll 

 of the vegetable cell. A singular 

 theory regarding them was broached 

 about four years ago by Dr. Karl 

 Brandt, who considered them as par- 

 asitic algtE, and even bestowed upon 

 them a generic and specific name, that 

 ot Zoochlorella conductrix. This 

 theory has been very forcibly assailed 



Explanation 



Fig. 17. Hydra viridis, expanding its tentacles, 

 X 29 diatn. 



Fig. 18. Tentacles and mouth H. viridis 5 mirutes 

 after being cut from the body, X 29 diam. 



Fig. iQ. Part of transverse section of body (after 

 Kleinenberg), X 67 diatn. 



Fig. -JO. Transverse section of ectoderm (alter 

 Kleinenberg), X 166 diaiii. 



Fig. 21. Neuro-muscle cells (after Kleinenberg), X 

 166 diatn. 



Fig. 22. Nemato cyst or thread cell, X 200 diatn. 



Fig. 23. Hydra viridis with parasitic trichodinae, 

 X 29 diam. 



Fig. 24. Trichodina pedicuhis Ehr., lateral view, 

 X 150 diam. 



OF Plate. 



Fig. 25. Trichodina pediculus Ehr., under side, X 

 150 diam. 



Fig, 26. Hydra copied from original drawing of 

 Leenwenhoek.* 



Abbreviations Used in all the Figures. 

 Ec. Ectoderm. 

 En. Endoderm. 



S. C. Spermatic Capsule ^testis. 

 O. Ovary. 



Me. Nerve nuiscle cells. 

 It. Interstitial layer of cells at base of ectoderm. 



* From photograph by author, from original paper 

 in Philosophical Transactions. 



