340 DR. N. ANNANDALE ON 



which are laterally expanded or bifid distally. The gonads are confined to the upper 

 part of the body in both sexes. Budding takes place very sparingly, in a definite zone 

 nearer to the aboral pole than to the mouth. The colour is never that of chlorophyl. 

 The above description will serve as a diagnosis of the form. It is based on the 

 examination of a large number of individuals taken during the years 1904-5 and 

 1905-6 in Calcutta. The several structures of Hydra orientalis may now be discussed 

 in greater detail. 



Body — 



Especially below the budding zone, the walls of the body are thin. The alimentary 

 canal is of considerable relative diameter, terminates bluntly below, and may be slightly 

 expanded at the base. Although it is not constricted at any point, undigested food does 

 not pass freely down it but remains in the upper half, giving temporarily to the body 

 the shape of a wine-glass. 



The external surface is not smooth but bears a delicate, raised reticulation, which 

 is more conspicuous below the budding zone than above it. The cnidocils of the nema- 

 tocysts are sufficiently long and numerous to give the upper part of the body a some- 

 what hirsute appearance under a low power of the microscope. 



Both ectoderm and endoderm cells are normal in character. 



Tentacles — 



Except when completely retracted, the tentacles are very slender. When fully 

 elongated they have the appearance of a number of minute beads strung loosely on an 

 almost invisible thread ; but I have not seen them elongated to such an extent as to 

 become quite invisible to the naked eye at any point. The terminal bead is longer, but 

 has not a greater transverse diameter than the others. The beads are batteries of sting- 

 ing cells set in ordinary ectoderm and supplied with nerve cells. These batteries do not 

 form uninterrupted bands round the tentacle, but each of them consists of several 

 transversely elongated tracts closely pressed together. Each tract surrounds the ten- 

 tacle incompletely and overlaps the one next to it at one end or at both. 



I have not seen an individual which was budding and yet had fewer than five 

 tentacles, or more than six ; the great majority of those examined have had six. Buds, 

 on the other hand, usually have five. On one occasion an individual which had only 

 four tentacles commenced (probably in abnormal circumstances) to develop male organs ; 

 two individuals while under observation appeared to bear as many as ten tentacles 

 each, until a microscopical investigation revealed the fact that reproduction by vertical 

 splitting had commenced, and that the crown of tentacles was really double. 



Nematocysts — ' r 



These structures are probably smaller in H. orientalis than they are in some spe- 

 cies ; I do not think that the size of the large cells is constant, but that it varies consider- 

 ably in different individuals. The thread is extremely long in all cases. The largest 

 type of stinging thread has a long neck set with a large number of very short, stout 



