Ji ' PROFESSOR ALLMAN. 



masses of protoplasm, quite destitute of investing membrane. 

 In the tentacles and basal portion of the animal each encloses 

 a vacuole, which is filled with a clear fluid, which, in its 

 behaviour with reagents, scarcely differs from pure water. 

 In the cells of the stomach-region there is no constant vacuole, 

 these cells being here usually in the condition of solid proto- 

 plasm masses. 



Imbedded in the protoplasm of the endodermal cells of 

 H. viridis there occur not only the nucleus, but the green 

 granules. These have a diameter of 0'009 mm. They con- 

 sist, fundamentally, of a firm mass, very rich in albumen, 

 coloured dark brown by iodine and deep red by carmine or 

 aniline. Lying over this is an exceedingly thin layer of green 

 colouring matter, which, in its optical and chemical proper- 

 ties, is intimately allied to the chlorophyll of the vegetable 

 cell, if it be not absolutely identical Avith it. It will be here 

 seen that the conclusions of Kleinenberg correspond with 

 those of Cohn, who had already maintained, as the result of 

 careful investigation, the identity of the green matter of 

 Hydra, and of certain green infusoria Avith the chlorophyll of 

 plants. 



With the green granules are also associated smaller cor- 

 puscles which have an angular shape, and instead of the pure 

 green of the others, possess a dark sooty colour. These are 

 frequently found conglomerated into heaps of very small, dark 

 brown or black granules. The free end of the cell never 

 contains chlorophylle granules; here, on the contrary, the 

 brown and black granules are accumulated. 



In Hydra aurantiaca and li. grisea the place of the chloro- 

 phyll spherules is taken by colourless, round or oval, firm 

 albuminous corpuscles, which are developed in the cells 

 forming the endoderm of the stomach cavity. Apart from 

 the want of chlorophyll, these are quite like the green cor- 

 puscles of H. viridis. They are also associated, as in the 

 latter species, Avith dark granules. In all the species fatty 

 particles and oil-drops are also found imbedded in the endo- 

 dermal protoplasm. 



In all parts of the body cavity certain cells of the endoderm 

 may be seen carrying a long very slender cilium ; rarely tAvo 

 such cilia may be found on one cell. The ciliated cells, hoAv- 

 ever, are isolated, and do not constitute a continuous ciliated 

 lining of the body cavity, and Kleinenberg calls attention to 

 the interesting analogy between this and an entirely similar 

 form of vibratile tissue (the Geisselzellen of Haeckel) which 

 occurs in the sponges. 



Such are the most important points of structure Avhich Ave 



