588 MONTGOMERY— MORPHOLOGY OF THE [April 24. 



garded the sericteries and tracheae as homologous, but questioned 

 whether the Malpighian vessels are related to them. Then, follow- 

 ing Semper's (1874) suggestion that the tracheae are metamor- 

 phosed segmental organs, Mayer (1875) went further in concluding 

 that the tracheae, sericteries and Malpighian vessels are homo- 

 dynamous and all homologous with nephridia of Annelids. Grassi 

 (1885) has in the main supported Mayer, in reasoning that the 

 Malpighian vessels, sericteries, the two transitory invaginations on 

 the head and the homodynamous tracheae are all probably excretory 

 in the larva; and (1888) supports the idea of the homology of 

 Malpighian vessels with tracheae on the ground that the former 

 occur in segments where the latter are lacking and are most abundant 

 when the latter are least numerous. But several strong objections 

 have been made to these comparisons, and especially by those who 

 have studied the embryogeny more in detail. Thus Hatschek 

 (1877&) has argued against the homology of the sericteries and 

 salivary glands with the tracheae, that in the segments where the 

 former occur tracheal invaginations are formed independently of 

 them. Then Palmen (1877) concluded that the Malpighian vessels, 

 developing from the proctodaeum, were originally hypodermal 

 glands that have come to group themselves around the inner end 

 of the proctodaeum and that their number is " in no way dependent 

 upon the number of particular body segments " ; while against the 

 homology of the tracheae with nephridia, he adducted the case of 

 their coincident segmental occurrence in Peripatus. Wheeler also 

 (1893a) judged that if the Malpighian vessels are homologous with 

 nephridia they can be only with the ectoblastic portion of the latter; 

 and that they are not homodynamous with tracheae, but rather with 

 the mass of oenocytes that represent the ectoblastic remains of 

 nephridia. Heymons (1896) also concluded that the Malpighian 

 vessels are not to be compared with nephridia, that they are only 

 local evaginations of the hind-gut. 



The evidence is that the Malpighian vessels are certainly not 

 homologous with annelidan nephridia, because they are strictly 

 ectoblastic and are not segmental. Their resemblance to the 

 sericteries and tracheae is only a very general one in that all of 

 these are ectoblastic invaginations, so that at the most we must 



