ADDRESS. 5 



or definite form, are eminently characteristic of protoplasm in some of 

 its simplest conditions. They have been termed ' Pseudopodia,' and will 

 frequently come before you in what I have yet to say. 



To the little protoplasmic lumps thus constituted, Haeckel has given 

 the name of Protamoeba primitiva. They may be compared to minute 

 detached pieces of Bathybius. He has seen them multiplying themselves 

 by spontaneous division into two pieces, which, on becoming independent, 

 increase in size and acquire all the characters of the parent. 



Several other beings as simple as Protamoeba have been described by 

 various observers, and especially by Haeckel, who brings the whole 

 together into a group to which he gives the name of Monera, suggested by 

 the extreme simplicity of the beings included in it. 



But we must now pass to a stage a little higher in the development 

 of protoplasmic beings. Widely distributed in the fresh and salt waters of 

 Britain, and probably of almost all parts of the world, are small particles 

 of protoplasm closely resembling the Protamoeba just described. Like it, 

 they have no definite shape, and are perpetually changing their form, throw- 

 ing out and drawing in thick lobes and finger-like pseudopodia, in which 

 their body seems to flow away over the field of the microscope. They 

 are no longer, however, the homogeneous particle of protoplasm which 

 forms the body of Protamoeba. Towards the centre a small globular mass 

 of firmer protoplasm has become differentiated off from the remainder, and 

 forms what is known as a nucleus, while the protoplasm forming the extreme 

 outer boundary differs slightly from the rest, being more transparent, 

 destitute of granules, and apparently somewhat firmer than the interior. 

 We may also notice that at one spot a clear spherical space has made its 

 appearance, but that while we watch it has suddenly contracted and 

 vanished, and after a few seconds has begun to dilate so as again to come 

 into view, once more to disappear, then again to return, and all this in 

 regular rhythmical sequence. This little rhythmically pulsating cavity is 

 called the ' contractile vacuole.' It is of very frequent occurrence among 

 those beings which lie low down in the scale of life. 



We have now before us a being which has arrested the attention of 

 naturalists almost from the commencement of microscopical observation. 

 It is the famous Amoeba, for which ponds and pools and gutters on the 

 house-roof have for the last 200 years been ransacked by the micro- 

 scopist, who has many a time stood in amazement at the undefinable form 

 and Protean changes of this particle of living matter. It is only the 

 science of our own days, however, which has revealed its biological im- 

 portance, and shown that in this little soft nucleated particle we have 

 a body whose significance for the morphology and physiology of living 

 beings cannot be overestimated, for in Amoeba we have the essential 

 characters of a cell, the morphological unit of organisation, the physio- 

 logical source of specialised function. 



The term ' cell ' has been so long in use that it cannot now be displaced 

 from our terminology ; and yet it tends to convey an incorrect notion, 



