96 THE RADIOLARIA 



protoplasm and its secretions are the product of intracapsular 

 activity. The extracapsular cytoplasm, on the other hand, has 

 no such regenerative power. When detached from the capsule it 

 loses its form, the pseudopodia contract, the vacuoles burst, and 

 the plasma undergoes granular degeneration. For this and other 

 reasons we may speak of the extracapsular cytoplasm as the ecto- 

 plasm, and the intracapsular plasma as the endoplasm ; for although 

 the pseudopodia are common to both and interconnect them, yet 

 the mass of the calymma is a secretion specialised for contact with 

 the outer world, and performs other important functions, whilst the 

 endoplasm is less directly concerned with the immediate physiological 

 needs of the animal. 



Bionomics. The most remarkable physiological characteristic 

 of Thalassicolla is its paucity of reaction. It possesses no power 

 of active movement, and responds only to two forms of external 

 stimulus vibration and heat ; and to one internal agency, namely, 

 the stimulus of reproduction. Under the influence of wave-action 

 Thalassicolla sinks till a calm stratum is reached, and then after a 

 time ascends to the surface. Towards small variations of temperature 

 it remains as inert as toward all conditions of illumination that 

 have so far been tried ; but a long-continued application of tempera- 

 tures above 30 C. or below 2 C. induces a descent from the 

 surface of the sea-water, and this is followed by the death of the 

 animal. The onset of maturity is also correlated with a descent 

 into deep water. During the nutritive phase and under normal 

 variations of vibration, heat, and light, the station of TJialassicolla is 

 at or near the surface of the sea. 



This station is ensured for it by the development of the calymma. 

 The mass of this veil is made up of a mucilaginous secretion containing 

 fluid-vacuoles, and is enclosed in a delicate cytoplasmic investment, 

 the quantitative proportion of which is in minimal relation to the 

 bulk of its secretions and vacuolar fluid. By careful observation, 

 weighings, and experiment, Brandt (24) has shown that the vertical 

 movement of Thalassicolla is due to the formation and expulsion 

 of vacuolar fluid. The hydrostatical requirements of the case 

 demand that, for flotation at the surface, the density of this fluid 

 should be that of water saturated with carbonic acid. As the 

 physiological probability is in favour of this conclusion, we may 

 accept Brandt's view as in all likelihood correct. Assuming 

 this, then, the explanation of passive descent and ascent is easy. 

 In calm weather and through a considerable range of temperature 

 the interchange of fluid between the vacuole and the sea is gradual, 

 and the slight wave-motion reinforces the calymma by acting as a 

 stimulant. Thus we may assume the balance of loss and gain, and 

 with it the surface position, are maintained. But the movements 

 of larger or more frequent waves, or the extremes of experimental 



