DEVELOPMENT OP THE CAPE SPECIES OF PEFJPATUS. 387 



The internal vesicle, which, together with the communica- 

 ting tube, has hitherto been overlooked, persists in the adult, 

 and probably constitutes an important functional part of the 

 salivary gland. 



Somites of the first, second, and third Legs (Part III, p. 

 507 et seq.). — The third, fourth, and fifth somites divide early into 

 a dorsal and ventral portion, of which the dorsal vanishes, while 

 the ventral acquires an opening to the exterior and persists as 

 the nephridium. The condition of these nephridia in Stage f 

 is shown by Part III, fig. 40. The subsequent changes are 

 very slight, and may be gathered from an inspection of 

 PI. XXVII, fig. 10, which is from a transverse section through 

 the third leg of an embryo almost ready for birth. The 

 nephridium (PI. XXVII, fig. 10) consists of a thin-walled 

 internal vesicle contained in the leg compartment of the body 

 cavity and communicating by a straight tube with the exter- 

 nal opening on the ventral surface. The wall of the vesicle 

 consists of a ragged protoplasmic layer, with here and there a 

 round nucleus. 



Somites of Legs 4 to 12. — The early history of the seventh 

 to the fifteenth somites inclusive is similar to that of the somites 

 of the first three legs ; but in the later stages the tubular part 

 of the nephridium becomes elongated, coiled, and divided into 

 at least three regions (PI. XXIX, fig. 17, diagram). (1) The 

 part next the external opening is dilated into a vesicle — the 

 external vesicle — which is connected with the external opening 

 by a narrow tube (PI. XXVII, fig. 11). (2) The vesicle opens 

 into a long coiled tube, which forms the greater part of the 

 nephridium. It is cut across twice in the transverse section 

 from which fig. 11 was taken. It is continuous with (3) a 

 short terminal portion in which the nuclei are very closely 

 packed together. This terminal portion opens with everted 

 lips into the thin-walled, internal vesicle, and constitutes the 

 so-called funnel of the nephridium. The external opening 

 of the nephridia of the fourth and fifth legs are at first imme- 

 diately outside the nerve cord, as in the case of the others. 

 Their adult position is due to a secondary shifting. 



