OBSEEVATIONS ON THE VOLVOCACEAE. 335 



bottom of the dish ; and inside each case was a Ghironomus larva 

 which escaped out on being disturbed with a needle. An examination 

 of a green case showed that it was made up of large numbers of 

 Pandorina colonies. The larva on being examined under the micros- 

 cope showed that it had been feeding on these Pandorina colonies ; 

 for its alimentary canal was full of them. 



Another curious phenomenon noticed by me was a tiny unicellular 

 Blue Green Alga attached to the body of a Ohlamydomonas. This 

 Blue Green Alga was evidently getting a free ride at the expense of the 

 Ohlamydomonas and benefiting by the advantages of the locomotion, 

 viz., better aeration and better food supply. Often there was more 

 than one rider on a single Ohlamydomonas, sometimes as many as five 

 or more. I occasionally came across a few cases where the riders 

 were too many in number for the poor Ohlamydomonas to carry, which 

 was therefore unable to move at all. 



Summary 



The following members of the Volvocaceae have been collected 

 from Madras : --Ohlamydomonas, Carteria, Gonium, Pandorina, E ado - 

 rina Pleodorina and Volvox. The last two are generally very rare 

 forms. 



Though thase forms may occur in various parts of the year and 

 in various situations, they attain their greatest luxuriance only in the 

 many small rain-water pools formed by the showers of the Summer 

 Monsoon season which at Madras are generally light and irregular, 

 though frequent. 



The organisms seem to like light of moderate intensity. They 

 come up sometime after sun-rise and if, in the middle of the day, the 

 sun-light is too strong, recede below and come up again towards the 

 latter part of the day and form a thick green film on the surface. In 

 this condition the organisms are generally very inactive. They sink 

 down again during the night. If the weather is cloudy they do hot 

 sink down in the middle of the day, nor do they float up, towards the 

 evening to form a film, but are active throughout the day. 



In certain rain-water pools formed in the Madras Beach, these 

 organisms are often found in large numbers on the wet sand around 

 the pool giving it a green colour. This situation is sought by them 

 probably for securing better aeration. In one of these pools where 

 the water had disappeared the wet sand was greenish, and its greenness 

 was due to many quiescent Chlamydomonadine cells without cilia, 

 This invasion of a sub-aerial region by a free swimming aquatic form 

 suggests how some sub-aerial unicellular Green Algae might have 

 originally evolved from some free swimming Chlamydomonadine type. 



