Chap. XI.] GENERAL SUMMARY. 215 



in the cells of the glands, the contents of which first become 

 cloudy; and this has been observed within 10 s. after a 

 gland has been excited. Granules just resolvable under a 

 very high power soon appear, sometimes within a minute, in 

 the cells beneath the glands; and these then aggregate into 

 minute spheres. The process afterwards travels down the 

 tentacles, being arrested for a short time at each transverse 

 partition. The small spheres coalesce into larger spheres, or 

 into oval, club-headed, thread- or necklace-like, or otherwise 

 shaped masses of protoplasm, which, suspended in almost 

 colourless fluid, exhibit incessant spontaneous changes of 

 form. These frequently coalesce and again separate. If a 

 gland has been powerfully excited, all the cells down to the 

 base of the tentacle are affected. In cells, especially if filled 

 with dark red fluid, the first step in the process often is the 

 formation of a dark red, bag-like mass of protoplasm which 

 afterwards divides and undergoes the usual repeated changes 

 of form. Before any aggregation has been excited, a sheet 

 of colourless protoplasm, including granules (the primordial 

 utricle of Mohl), flows round the walls of the cells; and this 

 becomes more distinct after the contents have been partially 

 aggregated into spheres or bag-like masses. But after a 

 time the granules are drawn towards the central masses and 

 unite with them; and then the circulating sheet can no 

 longer be distinguished, but there is still a current of trans- 

 parent fluid within the cells. 



Aggregation is excited by almost all the stimulants which 

 induce movement; such as the glands being touched two or 

 three times, the pressure of minute inorganic particles, the 

 absorption of various fluids, even long immersion in distilled 

 water, exosmose, and heat. Of the many stimulants tried, 

 carbonate of ammonia is the most energetic and acts the 

 quickest; a dose of ttAutt of a grain (.00048 mg.) given to 

 a single gland suffices to cause in one hour well-marked 

 aggregation in the upper cells of the tentacle. The process 

 goes on only as long as the protoplasm is in a living, vigor- 

 ous, and oxygenated condition. 



The result is in all respects exactly the same, whether a 

 gland has been excited directly, or has received an influence 

 from other and distant glands. But there is one important 

 difference; when the central glands are irritated, they trans- 



