THE COMMON HYDRA OF BENGAL. 343 



but a variety (bakeri, Marshall) l of H. viridis occurs in brackish water in England. 

 Recently (March 3rd-6th) I have examined living specimens, which appear to be 

 identical with the Calcutta form, at Chakradharpur in Chota Nagpur. All of them 

 were small and almost colourless, with five tentacles, and none were breeding. Mr. 

 C. A. Paiva, Entomological Assistant in the Indian Museum, at the same time collected 

 others, most of which had six tentacles, at Adra in the Manbhum District of Bengal. 

 These too were not sexually mature. 



I have no positive information as to the distribution of the form orientalis outside 

 Bengal. The living individuals examined at Pusa were stouter and of a more bril- 

 liant orange-brown than any I have seen in Calcutta, and bore four buds. Several 

 which were brought to Calcutta, however, became paler and more attenuated within 

 three days. It would therefore seem that the individuals living at Pusa are naturally 

 more robust than those living in Lower Bengal, probably because the temperature of 

 Northern Bihar is considerably lower than that of Calcutta, at any rate in winter. 

 Whether or no the Pusa race differs constantly in any respect from that of Calcutta 

 it is as yet impossible to say. 



None of the specimens of Hydra which have been recorded from Southern Asia 

 have been chlorophyl-green in colour. It is probable therefore that the true Hydra 

 viridis does not occur in India or the surrounding countries ; but it is not known how 

 many forms do occur in Southern Asia. Possibly the only one is that which I 

 have named Hydra orientalis. 



II. 



The statements in this section of the paper are based, as far as possible, on obser- 

 vations made on specimens living in natural conditions. 



Throughout the winter of 1905-6, from November till April, individuals have been 

 taken several times a week from the Museum ' ' tank,' ' a deep, natural pool of about 

 half an acre's area, and have been examined immediately; while during the cor- 

 responding period in 1904-5 more casual investigations were made. During the first half 

 of May in the present year only a few individuals were obtained, but a consider- 

 able number have been taken during the later part of the same month and in June. 

 In this way many hundred individuals have been observed. Attempts to keep speci- 

 mens in captivity under normal circumstances have also been made, with fair success 

 in cooler weather, but with almost complete failure during a rise in temperature, 

 especially if the rise was sudden and considerable, and during the hot weather. 

 The reason of this difficulty will be dealt with later under the heading ' Favourable 

 and Unfavourable Conditions. 



Reproduction. 



Hydra orientalis, like other forms of the genus, reproduces its kind in three ways : — 

 (1) by fission ; (2) by budding ; and (3) by fertilized eggs. 



I Zeitschr. f.wiss.Zool., XXXVII, 1882, p. 666. 



