48 Coelenterata. 



long as the others. By means of an oblique incision both results can be obtained 

 in a single animal. This distension of the coelenteron with fluid is necessary 

 for the persistence of the body wall and tentacles. - - See also Rand. 



Bohn( 2 ) points out that a series of stimuli applied at short intervals may 

 produce 3 different effects (1) constantly increasing, (2) first increasing later 

 decreasing, (3) constantly decreasing. These may all be seen in the same 

 organism according to the internal chemical or external conditions. E.g., the 

 tentacles of Cerianthns on being touched bend towards the mouth. At 6 a. m. 

 (in September) the responses were of the first type; later in the morning, of 

 the second type; and in the evening the tentacle became insensible. The more 

 illumination received, the more rapidly insensibility ensued. These differences 

 depend on the amounts of photo-chemical substances present at the different 

 periods. 



Pieron holds that neither light nor depth of water is the factor which regu- 

 lates the expansion or contraction of Actiniae, and that a position half out of 

 the water ensures an anemone complete resistance to asphyxia. Oxygen seems 

 to be directly important and is also potent because it brings about oxidation 

 of waste products. The action of C0 2 appears doubtful. Actinias from a low 

 zone of the littoral region close much less readily than those from a higher 

 zone. - See also infra, Mollusca p 4, Pieron ( 2 ). 



Uexkull describes experiments on Ammonia sulcata. The tentacles contract 

 only when struck forcibly or rubbed with a piece of sterilised sponge. Local 

 pressure produces diminution of muscular tonus and dilatation of the muscles. 

 Dilute acetic acid acts on the circular muscles ; a local excitation produces 

 peripherally a contraction and centrally a relaxation, a general one the con- 

 traction of all the circular muscles. Chemical irritation renders the tentacle 

 very sensitive to mechanical stimuli; during the former it elongates owing to 

 contraction of its circular muscles; if mechanical irritation be now added the 

 tentacle shortens, because its longitudinal muscles contract. Excitation by means 

 of food acts on the cutaneous glands and the food sticks to the tentacle. The 

 responses to these 3 modes of stimulation show that there are 3 plexuses of 

 nerves, for the longitudinal and circular muscles and for the cutaneous glands 

 respectively. 



Cooper shows that the polyps of Bathypathes patula, each of which is divided 

 into 3 portions, present great differences according to the state of their sexual 

 maturity. When the gonads are small, the 3 parts - - the 2 gonozooids 

 and the gastrozooid - - stand up well separated from each other. Later, as 

 the ova begin to form, the sexual portions of the polyp become gradually 

 swollen out into a sac and the gastrozooid appears to degenerate, for in the 

 final stage it is non-existent, while the gonozooids have the appearance of 2 egg- 

 sacs, their tentacles having disappeared. In one of the colonies examined, 

 2 (or 3) neighbouring branches of one side have adhered together from their 

 ends backwards over a considerable proportion of their length. There is an 

 actual concrescence accompanied by breaking down of tissue elements. The 

 polyps of a colony are all at the same stage of sexual maturity. When the 

 colony becomes ripe the ova are liberated by rupture of the polyp walls, and 

 the colony probably dies. The author describes Stichopathes 8 (5 n.), Cirri- 

 pathcs 1, Schizopathes 1, Bathypathes 1, Aphanipathes 2 n. and Antipatlies 10 

 (5n.). - See also Roule( J ) and Silberfeld( 1 , 2 ). 



Gardiner regards the patella group of Fungia as the central form from 

 which all the others originated. First the diaseris group separated in late Eocene 

 or early Miocene times, then, at the commencement of the Quaternary period, 



