C. F. ROUSSELET ON TRIARTHRA BRACHIATA. 145 



victim, and Triarihra can then be seen in its enemy's stomach, 

 with the lon^ spines protruding through the oesophagus and 

 mouth. Triarihra cannot therefore escape its enemies by flight, 

 but rather by rendering itself unapproachable and impregnable, 

 much in the same way as the porcupine and hedgehog, and it is 

 evident that the longer the spines the greater is the protection 

 they afford. It is ludicrous to see little Ti'iarthra hrevispina, 

 with its tiny spines, act exactly like the long-spined species, 

 though its small spines cannot be of much use when Asplanchna 

 is the enemy. 



The greatest enemy to all species of Triarthra is undoubtedly 

 the surface-film of the water, for though these creatures live in 

 the water, the surface of their bodies and spines is strongly water- 

 repellent. The moment any of these animals touch the surface- 

 film they adhere there so firmly that no efforts of theirs can 

 disengage them, and they must perish. The same is the case 

 with a good many other rotifers, particularly Polyarthra, Anuraea 

 longispina, Pedalion, and Mastigocerca, and also with some 

 Cladocera, such as Bosmina. Sometimes I collect very large 

 numbers of Triarthra longiseta and T. niystacina, and after 

 keeping these a few days in a small aquarium, the surface-film 

 is covered by quite a layer of their dead bodies. 



Explanation of Plate 8 (Lower Portion). 



Fig. 7. Triarthra hrachiata, n. sp. $ , ventral view, x 370. 

 „ 8. „ „ resting egg x 300. 



