m 



PSYCHE. 



[December 1S93. 



out* that the sexual ducts arise in Xiph- 

 idium as hollow diverticula of the 

 somites, like the nephridia and sexual 

 ducts of Peripatus. It is, however, only 

 the mesodermal portion of the nephridia 

 which arises in this way ; if what stu- 

 dents of annelid development tell us 

 prove to be correct, each nephridium 

 must also have a small proximal piece 

 derived from the ectoderm. The oeno- 

 cyte cluster may be this piece disinte- 

 grated and changed in function. I deem 

 it probable that the insect nephridium 

 has passed through the following stages : 



1. The nephropore (now represented 

 by the oenocyte pit in the embryo) 

 became occluded and then obliterated 

 together with the lumen of the ectoder- 

 mal portion of the nephridium. 



2. With further degeneration the 

 ectodermal and mesodermal anlagen of 

 the nephridium failed to unite during 

 ontogeny and persisted as separate 

 structures. 



3. These two anlagen took on new 

 functions — the ectodermal or oenocyte 

 portion acquiring some function 

 perhaps analogous to that of the 

 thymus in vertebrates ; the mesodermal 

 portion becoming converted partly into 

 the corpora adiposa and in part into the 

 sexual ducts. | 



*A contribution to insect embryology. Journ. ct 

 morph. vol. viii, no. I. 1S93, p. 116 et seq. 



f The fat-body retains to this day a nephric function 

 inasmuch as it stores up urates often in considerable 

 quantity. Kowalevsky (Ein beitrag zur kenntnis der 



The Malpighian vessels, if at all com- 

 parable to nephridia, can represent only 

 the ectodermal (oenocytic) ends. On 

 the trisegmental hypothesis the vessels 

 would be equivalent to three pairs of 

 oenocyte-clusters, which had preserved 

 their tubular character and excretory 

 function. But the great difficulty lies 

 in understanding the process whereby 

 these three pairs of metameric and 

 originally integumental structures could 

 be carried into the anal invagination 

 and appear ontogenetically as hollow 

 buds at its inner end. On the other 

 hand my hypothesis is beset with fewer 

 difficulties, if we suppose that the three 

 pairs of Malpighian vessels do not rep- 

 resent three metameres, but only a single 

 one, for it is easy to understand how a 

 single pair of oenocyte tubules could be 

 carried in and subsequently, in the re- 

 mote ancestors of existing insects, give 

 rise to three pairs of vessels by a simple 

 process of budding. 



These considerations lead me to 

 reject the trisegmental hypothesis and, 

 while regarding 6 as the primitive 

 number of Malpighian vessels in insects, 

 to postulate only a single pair in more 

 ancestral Artie ulata. 



The University of Chicago. 



Sept. 1S92. 



exkretionsorgane. Biol, centralbl. bd. ix, 1S90, p. 42 et 

 seq.) in a long series of experiments found that 

 carmine, chloride of iron, and litmus were abstracted 

 from the blood by the cells of the pericardial fat-body. 

 In Muscid larvae the cells of the garland-shaped strand 

 have a similar function. 



