larva is provided with nearly the full number of feet on the rest 

 of the body, there being no metamorphosis. The body, at first 

 cylindrical, afterwards becomes flattened. Thus the Centipedes 

 may be said in some degree to pass through a Julus condition, 

 and at all events, both morphologically and embryologically, the 

 Centipede is a more highly developed creature than the Thousand- 

 legs, a view we have always taken, but felt was rather based on a 

 priori conceptions than on a sure basis of facts, now happily af- 

 forded by the beautiful researches of Metschnikoff. To sum up 

 the phases of development of the Myriopods we have, then : — 



1. Morula stage. 



2. A hexapod larva (Leptus form) as in the Thousand-legs ; or, 

 as in the Centipedes, there is no metamorphosis, the young being 

 like the parent. 



3. Adult. 



Development of the Mites. Coming now to the mites and spi- 

 ders, we find some peculiar features in the life-history of the 

 former which deserve attention, though space compels us to be 

 brief at the risk of being obscure. Most mites pass through a 

 metamorphosis, some undergoing striking changes within the egg. 

 For example, the Atax Bonzi, which is a parasite on the gills of 

 fresh water muscles, first hatches in an oval form enveloped in 

 a membrane (deutovum). From this "deutovum " is developed a 

 six-footed larva. In this second larva state it is free, moving over 

 the gills of the mussels, finally boring into the flesh of its host to 

 undergo its next transformation. Here the young mite increases 

 in size and becomes round. The tissues soften, the limbs are 

 short and much larger than before, the animal assuming an em- 

 bryo-like appearance, and moving about like a rounded mass in 

 its enclosure. After a moult it assumes the so-called " pupa- 

 state." During this process the limbs grow much shorter and :.iv 

 folded beneath the body, the animal being immovable, while the 

 whole body assumes a broadly ovate form, and looks like an em- 

 bryo just before hatching, but still lying within the egg. 



In the genus Myobia, a parasite of the European field-mouse, 



