468 Miss M. Greenwood. On the Constitution and [Dec. 14, 



point have been apparently in the condition in which they left the 

 oesophagus, are rearranged in a very remarkable fashion. The solid 

 particles, it may be of proteid, of pigment, or bacteria, are gathered to a 

 cluster, with a rapid centripetal movement; those which are more peri- 

 pheral leave the boundaries of the vacuole, and a composite solid mass lies 

 in clear fluid surroundings. The outline of constituents so strikingly 

 individual as are bacteria or the fat globules of milk may still be 

 made out in the cohering cluster, but Brownian movement is ended, as 

 are the " proper " movements of any small organisms which may be 

 present, and further change is not in the direction of freedom, but makes 

 the union closer ; it tends to perfect the homogeneity of the composite 

 solid. To this rearrangement of matter I apply the term " aggrega- 

 tion,"* for the obvious feature of the act is the clustering of particles 

 of matter which were scattered before. It is most clearly demonstrable 

 in vacuoles which contain but few minute particles suspended in a 

 relatively large amount of water ; it is masked when the solid matter 

 preponderates or is less finely divided. No distinct relation can be 

 traced, however, between the chemical character of the ingested 

 matter and energy of aggregation, for nutritious and innutritious 

 particles are moved with equal vigour and show equally little ten- 

 dency to immediate subsequent separation. I might enumerate no 

 inconsiderable number of variations of this process, some dependent 

 on peculiarities of the ingesta dealt with (the presence of organic 

 matter in solution, the rare enclosure of filamentous bacteria), some 

 related rather io changes in the condition of Carchesium (abnormally 

 eager ingestion or exceptionally lethargic action), but through all the 

 modifications I have observed the salient characteristic of aggregation 

 of solids and synchronous separation of fluid may be traced, and in 

 face of each, the question arises, " What force effects this movement and 

 insures this redistribution of matter ? " 



In answer to this question, three hypotheses may be considered : 

 1. It may be supposed that as particulate proteid matter if pressed 

 together with some force tends to form masses which cohere after 

 the pressure is removed, so in the vacuole of ingestion the approxi- 

 mately symmetrical discharge of small jets of fluid from, the sur- 

 rounding protoplasm carries solid particles centripetally, and that, 

 after displacement of the water between them, they cohere. It is 

 noticeable, however, that grains of Indian ink may be united firmly 

 in aggregation and discharged as a solid mass, that relatively large 

 granules (such as the fat drops of milk) are inseparable after the first 

 marked centripetal shifting, f and that nothing is more striking than 



* I use this term with, some reluctance in face of the fact that it was applied by 

 Darwin many years ago (' Insectivorous Plants ') to an entirely different process in 

 the cells of the tentacles of Drosera. 



f It will be gathered from what has been said above that only when these 



