THE NEPHBIDIA. 137 



cord and salivary glands lie). In addition to these there are 

 the leg cavities, which contain the nephridia and communicate 

 with (4). Of these the central compartment, lateral sinuses, 

 and heart are free for the most part from traversing tissue, 

 while the pericardial chamber and the leg cavities are broken 

 up by reticular tissue, and the leg cavities by muscles as well. 



The Nephridia, 



An account of the nephridia up to Stage f will be found in 

 Ch. IV. By Stage o they have practically attained the adult 

 condition, and to complete ray account of their history it will 

 only be necessary to describe their final condition, for which 

 purpose I have chosen a stage shortly before birth. I propose 

 at the same time to give a short recapitulatory account of their 

 whole history, under the head of the somites from which they are 

 respectively derived. The general changes which the somites 

 undergo will be rendered clear by a glance at the diagrams 

 on PI. XIII, figs. 14 — 17. It must be remembered that I 

 am only dealing here with the cavity contained in the somites, 

 i. e. the ccelom, and its immediate lining. The walls of the 

 somites, particularly the somatic walls, become greatly thick- 

 ened and hollowed out. The tissues and cavities so formed 

 give rise to muscles, connective tissue, and parts of the vascular 

 system, as has already been fully described. 



Somites of the Antenna (p. 86). — The first somites send 

 down a diverticulum outside the brain towards the skin (PI. 

 VII, fig. 19 b, PI. IX, fig. 50, «. so. 1) and then divide into 

 two parts (PI. IX, fig. 51, s. 1). They seem to have com- 

 pletely disappeared by Stage g. The ventral diverticulum of 

 Stage E is obviously the rudiment of a nephridium. 



Somites of the Jaws (p. 88). — The second somites do 

 not give rise to even a I'udiment of a nephridium. They 

 seem to disappear. 



Somites of the Oral Papilla (p. 75 et seq.). — The third 

 somites send out a ventral diverticulum (PI. VII, fig. 21 €.)> 



