50 HABITS OF WOKMS. Chap. I. 



free calciferous cells. As the smaller concre- 

 tions increase in size, they come into contact 

 and unite, thus enclosing the now functionless 

 lamellse ; and by such steps the formation of 

 the largest concretions could be followed. 

 Why the process regularly takes place in the 

 two anterior glands, and only rarely in the 

 four posterior glands, is quite unknown. 

 Morren says that these glands disappear 

 during the winter ; and I have seen some 

 instances of this fact, and others in which 

 either the anterior or posterior glands were 

 at this season so shrunk and empty, that 

 they could be distinguished only with much 

 difficulty. 



With respect to the function of the calci- 

 ferous glands, it is probable that they pri- 

 marily serve as organs of excretion, and 

 secondarily as an aid to digestion. Worms 

 consume many fallen leaves ; and it is known 

 that lime goes on accumulating in leaves until 

 they drop off the parent-plant, instead of 

 being re-absorbed into the stem or roots, like 

 various other organic and inorganic sub- 

 stances.* The ashes of a leaf of an acacia 



* De Vries, * Landwirtli. Jahrbiicher,' 1881, p. 77. 



