EXCRETOR Y ORG A N;S. 



573 



which joins the fourth section of it close to the opening into the 

 Wolffian duct (fig. 390 px). The remainder of the vesicle becomes 

 converted into a Malpighian 

 body {m.g). By the first of 

 these changes a tube is estab- 

 lished connecting each pair of 

 segments of the mesonephros, 

 and though this tube is in part 

 aborted (or only represented by 

 a fibrous band) in the anterior 

 part of the excretory organs in 

 the adult, and most probably in 

 the hinder part, yet it seems 

 almost certain that the second- 

 ary and tertiary Malpighian 

 bodies of the majority of seg- 

 ments are developed from its 

 persisting blind end. Each of 

 these secondary and tertiary 

 Malpighian bodies is connected 

 with a convoluted tubulus (fig. 

 391 ariKj), which is also deve- 

 loped from the tube connecting 

 each pair of segmental tubes, 

 and therefore falls into the primary tubulus close to its junction 

 with the segmental duct. Owing to the formation of the accessory 

 tubuli the segments of the mesonephros acquire a compound cha- 

 racter. 



The third section of each tubulus becomes by continuous growth, 

 especially in the hinder segments, very bulky and convoluted. 



she 



Fig. 390. Longitudinal vertical sec- 

 tion THROUGH PART OF THE MESONEPHROS OF 

 AN EMBRYO OF SCYLLIUM. 



The figure contains two examples of the 

 budding of the vesicle of a segmental tube 

 (which forms a Malpighian body in its own 

 segment) to unite with the tubulus in the 

 preceding segment close \o its opening into 

 the Wolffian (mesonephric) duct. 



ge. epithelium of body-cavity; st. peri- 

 toneal funnel of segmental tube with its 

 peritoneal opening; mg. Malpighian body; 

 px. bud from Malpighian body uniting with 

 preceding segment. 



Jimiy 



7>tCf 



Fig. 391. Three segments of the anterior part of the mesonephros of a 

 nearly ripe embryo of scyllium canicula as a transparent object. 



The figure shews a fibrous band passing from the primary to the secondary Mal- 

 pighian bodies in two segments, which is the remains of the outgrowth from the primary 

 Malpighian body. 



Ht.o. peritoneal funnel; -p.mg. primary Malpighian body; a.mtj. accessory Mal- 

 pighian body; w.d. mesonepliric (Wolffian) duct. 



