130 SUMMARY OF CUERENT RESEARCHES RELATING TO 



which fail to respond to stimulus when the animal is deeply anaesthetized. 

 Hence it is concluded that their action is primarily controlled by nerves. 

 Under ordinary stimulation their action is profound and lasting, and has 

 given grounds to the idea that the actinian muscle is specialized almost 

 exclusively on the side of its tonicity, 



A fourth type is seen in the transverse muscles of the mesenteries, 

 particularly of the complete mesenteries. When food- juice is discharged 

 on the tentacles or lips the transverse mesenteric muscles contract and 

 open the oesophagus, preparatory to what under normal circumstances 

 would be the swallowing of the food. On withdrawing the stimulus these 

 muscles quickly relax and the oesophagus closes. This reaction is so 

 definite and precise in its relation to the stimulus, and so invariable in its 

 occurrence, that it must be regarded as a true reflex. 



The muscular reactions thus range from direct muscle responses of a 

 most primitive character to true reflexes. The more complex operations 

 of food-taking, creeping, and so forth, depend upon some combination 

 of the various types of muscular or neuromuscular activity. These 

 operations are often extremely complex, and call for a high degree of 

 co-ordination ; and yet this co-ordination is almost entirely of local 

 origin, for an isolated tentacle will react to food almost exactly as an 

 attached one does, and the pedal disk, even after the oral disk has been 

 cut away, wdll creep in a fashion indistinguishable from that of an intact 

 animal. It may be concluded that the nervous system of the sea- 

 anemone is essentially diffuse, lacking obvious centralization. 



Sagartia parasitica Mounting Shells.*— H. N. Milligan describes 

 the way in which an isolated specimen of this sea-anemone, dropped into 

 an aquarium, adhered to the Nassa shell of a passing hermit-crab, and 

 gradually mounted it in about five minutes. It was removed from the 

 Crustacean and tried with an empty whelk-shell, which it also mounted. 



Porifera. 



Gelatinous Spicules in a New Genus of Siliceous Sponges.f — 

 Arthur Dendy describes Gollosclerophora arenacea g. et sp. n., a tetraxonid 

 sand-sponge with gelatinous microscleres (colloscleres). The normal 

 skeleton is almost entirely replaced by sand-grains. The megascleres are 

 slender strongyla, occurring chiefly in loose wisps radiating towards the 

 surface, where they form- sparse surface-brushes. The colloscleres 

 (0' 02-0 "OS mm. in length) vary in form. When contracted they 

 always show an indentation or notch on one side, and are sausage-shaped, 

 boomerang-shaped, and kidney-shaped. They swell up and become 

 gelatinous on the addition of water. They consist of colloidal silica, 

 and are formed by special scleroblasts as extracellular secretions. They 

 also occur in two other related sponges, as will be afterwards de- 

 scribed. It is probable that in life the swollen collosclere fills the 

 vesicle in which it lies. The wall of the vesicle may be regarded either 



* Zoologist, XX. (1916) pp. 39-40. 



t Proc. Key. Soc, Series B, Ixxxix (1916) pp. 315-22 (1 pi.). 



