ox DEVELOPMENT ETC. OF i'HOllOXI.S. 557 



4. Organs of JlcsoOladic Orujln. 



As the UR'Soblastic organs have been l)ul httle studied in their 

 development, so their strueture and fate after metamorphosis are 

 very imperfeetly known. Although I have endeavoured to make mv 

 study of the organs as exhaustive as possilde, some important 

 questions remain yet unsoh'ed. The prineipal organs to be des- 

 eribed in this place are the muscular elements, the vascular system, 

 and the iicpliridia. 



Nephridia. 1 will treat these imder the mesoblastic organs, 

 for, though the nephridial canals are of ectoblastic origin, the 

 organs as a whole bear intimate relations to the mesoblast. ]\Iost 

 of the earlier (jbservers overlooked the presence of nephridia in 

 the larva. The first discoverer was AVagexer ('48), whose descrip- 

 tion is, however, very meagre and gives us no exact idea of the 

 organ. Caldwell in his preliminary note ('82-'83) has given a 

 detailed description of the nephridia. According to his view, the 

 nephridial canal at no time during larval life, opens into the bodv- 

 cavity. 



Master.aiax ('97) has descril)ed the excretory system of the 

 larva in detail and has suggested an hypothesis which seems to 

 me to l)e an extraordinary one. Each of the three " segments " 

 of the larval body, he concludes, is provided with a paired organ 

 which perf )rms the excretory function. The three ])airs of organs 

 are called respectively the '' proboscis pores," the "collar nephridia," 

 and the '' trunk ne[)hridia," Of these, however, the presence of 

 the iirst and the third is, as I have before pointed out, very 

 doubtful. The second pair, or the collar ne[)hridia, are the organs 

 which I consider to be the nei)liridia. ^Mastekman's views on the 



