i 70 The Field Naturalist's Quarterly May 



fascinating study of embryology, but enough has been said to show how 

 important it is that we should have a clear idea as to 



What is a cell ? 



Briefly, a cell might be defined as 



The unit of organic life. 



Each cell consists usually of three portions — - 



1. An outer covering, or cell-wall, enclosing 



2. A mass of living matter, protoplasm (fig. 4 b), which again contains 



a more solid portion, 



3. The nucleus (fig. 4 c). 



Having settled these preliminaries, our best course will be next to 

 take an example. The simplest, and for many reasons the best, 



example is Amoeba — a creature which is 

 adopted in all biological text-books as a 

 type of a unicellular organism. It is, 

 however, an imperfect cell, as it has no 

 cell-wall. 



A certain cookery-book, when treating 

 of the proper procedure in preparing a 

 hare for the table, gives this sage advice, 

 " First catch your hare, then," &c. Echo 



Fig. 4. Amceba. now cr ' es > " First catch your Amoeba, 



then put him in the microscope." But 



a Contractile vacuole. v -> t 11 i ,1 



b Protoplasm. now • I we " remember, as a youth, 



c Nucleus. reading eagerly through the description 



of Amceba in a certain text-book, and 

 going forth to the nearest pond determined to catch one of these 

 wonderful beasts and carry it home captive. The book said it was 

 a bit of brown jelly to be found crawling on the surface of the mud at 

 the bottom of a pond. No idea was given as to size, and I expected 

 to find a creeping thing as big as a mustard-seed, if not as large as a 

 pea. I could see nothing resembling the pictures, but took some of the 

 weeds home, and put a piece in the microscope. What is this snaky 

 thing gliding across the field ? Surely it must be the long - sought 

 Amceba ? Not a bit of it. I had captured my first Hydra. Obviously 

 this was not the way to find Amceba, and it was many years later that I 

 first made personal acquaintance with it. To the practical field zool- 

 ogist who wants to find Amceba the best advice is to look for it in 

 ditches, not in ponds. Choose a ditch which is undisturbed, and which 

 contains clear water and growing weeds — duckweed, algae, &c. In the 

 summer when the sun shines the surface of the water will be covered 

 with a thin scum consisting almost entirely of the microscopic algae 

 called diatoms. Take some of this scum and some of the floating 

 weeds, and you are certain to find amongst the other organisms 

 hundreds, perhaps thousands, of Amoebae. 



Place a few drops of this gathering on a glass slip and examine in the 

 microscope with the i-inch objective. Even now it is no easy matter to 



