DEVELOPMENT OF THE CAPE SPECIES OP PER1PATUS. 385 



main chambers : (1) the central compartment of the body 

 cavity ; (2) the heart ; (3) the pericardial cavity ; (4) the two 

 lateral compartments or lateral sinuses (in which the nerve- 

 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 

 Part III. By Stage g they have practically attained the adult 

 condition, and to complete my 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. XXIX, 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 Antennae (Part III, p. 504). — The first 

 somites send down a diverticulum outside the brain towards 

 the skin (Part III, figs. 19 b, 50, s. so. 1) and then divide into 

 two parts (Part III, 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 (Part III, p. 506). — The second 

 somites do not give rise to even a rudiment of a nephridium. 

 They seem to disappear. 



