498 EDWIN S. GOODRICH. 



which description agrees with that of Laurie (72) of the origin 

 of the coxal gland in Scorpio, and of Kingsley (65) in Limulus. 



The genital cells are derived from the walls of the coelomic 

 follicles ^ of many segments (Heymons, 57; Wheeler, 105). 

 The dorsal portion of these follicles generally fuse to form con- 

 tinuous tubes, or a median genital sac (as in the Crustacea). 

 The ducts are the peritoneal funnels of one segment. The 

 particular segment selected, so to speak, for this purpose varies 

 much in position in different groups, and also according to sex. 

 Wheeler, in his admirable account of the development of the 

 Orthoptera (105), shows that the coelomic follicles of all the 

 abdominal segments at an early stage begin to develop peri- 

 toneal funnels, but that those of one segment only reach the 

 exterior and form the genital ducts (fig. 30). 



As far as we can see, therefore, there are no certain traces of 

 true nephridia in the Arthropoda. The segmental organs, the 

 green glands, the shell glands, and the genital ducts are all 

 developed as peritoneal funnels.^ 



SiPUNCULUS. 



The development of the excretory organ of Sipunculus 

 nudus has been described by Hatschek (53). The nephridium 

 arises from a large cell (? " funnel-cell ^' ) which comes to lie in 

 the wall of the coelomic follicle. This cell divides, forming a 

 chain of cells in which a lumen is developed. The outer end 

 joins and opens on to the epidermis; the inner end grows 

 towards and opens into the coelom. The ciliated funnel is 

 formed from the coelomic epithelium. From this it would 

 appear that the excretory organ of Sipunculus is of a double 

 origin, formed by the junction of the nephridium with the 

 peritoneal funnel, as in most Polychsetes. It functions as the 

 carrier of both genital and excretory products. 



' Sedgwick holds that tliey are, in Peripatus capensis, derived from the 

 hypoblast. If this be the case, it must be considered as due to some secondary 

 modification. 



- Tlie possibility of the segmental tracheae of the Arthropods being derived 

 from the true nephridia should not be lost sight of. The tracheJE arise com- 

 paratively late, as a rule, as invaginations of the epidermis, and it seems not 



