PHYSIOLOGY OF THE INVERTEBRATA. 



99 



The preceding table shows certain differences in the compo^ 

 sition of the different kinds of larval food, more especially in 

 the composition of the solids present. Its composition is^ 

 moreover, quite different from that of the bee's saliva, which 

 contains no sugar. The difference between the proportional 

 amount of the different solids present in the different forms 

 of larval food is a constant one, and no doubt this variation 

 has in view the particular requirements of the larvae in 

 question. Certain small but constant differences were also 

 observed in the chemical composition .of the food of the 

 larval drones during the first four days and at subsequent 

 periods. 



, Not only is there a difference in the quality, but there is 

 also one in the quantity of the food supplied. The juice 

 from lOO queen-bee cells yielded 3.6028 grammes of dry 

 matter, that from 100 drones' cells 0.26 12 gramme, and that 

 from 100 workers' cells, 0.0474 gramme. 



(f?) The Araneincc. — As the spider's web has indirectly to 

 do with digestion a few remarks on the subject may not be 

 out of place. There is no doubt that "one of the most 

 characteristic organs of the Araneincc is the arachnidium, or 

 apparatus by which the fine silky threads which constitute 

 the web are produced. H. Meckel,* who has fully described 

 this apparatus as it occurs in Upeira diadema, states that, in 

 the adult, more than a thousand glands, with separate 

 excretory ducts, secrete the viscid material, which, when 

 exposed to the air, , hardens into silk. These glands are 

 divisible into five different kinds, and their ducts ultimately 

 enter the six prominent arachnidial mammillas, which, in this 

 species, project from the hinder end of the abdomen. Their 

 terminal faces are truncated, forming an area beset with the 

 minute arachnidial papillae by which the secretion of the 

 glands is poured out." 



The secretion of these glands is insoluble in water, and has 

 a nitrogenous basis. Web-spinning has several objects in 

 * Miiller's ArcJiiv, 1846. 



