1907.] Records of the Indian Museum. 203 



dead zocEcia, but none were found actually in the course of develop- 

 ment. No sexually mature zocecia were observed. 



The form of the resting buds of Vidorella pavida is not without 

 a certain systematic interest, for not only do the^^ appear to exhibit 

 very distinct differences from those of Paludicella and Potsiella, 

 but their shape is not altogether dissimilar to that of the zocecia of 

 Hislopia. It is possible, judging from the analogy of other or- 

 ganisms found in stagnant water in Lower Bengal, that they are 

 produced both at the end of autumn and the beginning of spring, 

 both these seasons being critical periods in the life c^'-cles of many 

 of the lower invertebrates of the Calcutta tanks. If this is so, it 

 is probable that they do not undergo further development in the 

 one case until the cold weather is well established, and in the other 

 until the rains have lowered the temperature very considerably. 

 The dangers to be guarded against at the two periods are different. 

 In spring the approach of the hot weather not only raises the tem- 

 perature of the water but also, perhaps consequently, induces an 

 enormous multiplication of aquatic bacteria. Whether these bacteria 

 have any specific action on other organisms is not known, but their 

 rapid increase is accompanied by a simultaneous disappearance or 

 depauperation of many of the common aquatic invertebrates, while 

 the scum they produce on the surface certainly prevents aeration of 

 the water. In autumn, on the other hand, the risk of actual desic- 

 cation is great, for although evaporation is naturally more pro- 

 nounced in summer, it is, at this season, to some extent counter- 

 balanced by the heavy thundershowers that frequently fall ; 

 whereas in winter, during which there is usually very little rain, 

 the temperature is quite high enough to evaporate the water of 

 many of the smaller pools. 



Family VESicui^ARnD^. 



The characters of this family have been discussed by all those 

 who have dealt from a systematic point of view with the Ctenostomes 

 as a whole, but the tropical species are still far from being well 

 known. So far as they have been studied, they appear to be closely 

 related to, or in many cases identical with European forms. In the 

 East, as in Europe, members of certain genera are not averse to 

 * brackish water. It is worthy of note that Vidorella pavida was 

 originally found in England in the same locality as Bowerhankia 

 imbricata, a species allied to the one found with it in Lower Bengal. 



Bowerhankia caudata, Hincks. 



(B. caudata) Hincks, Brit. Marine Polyzoa, p. 521, pi. 75. 



I am indebted in the first instance for the identification of this 

 species to Miss L. Thornely. Mr. R. Kirkpatrick has also been 

 kind enough to examine specimens and is of the opinion that they 

 are identical with Hincks's species. A renewed search in the ponds 

 has proved it to be at least as abundant as Vidorella pavida, the 



