A SOUTH AMERICAN SPECIES OE PERIPATUS. 359 



therefore necessary to suppose that because a certain process 

 is brought about in the same way in two dissimilar forms, that 

 there must be some genetic connection between these two 

 forms. For instance, the same mechanical cause (i. e. loss 

 of yolk) has brought about remarkably similar results in 

 two entirely different groups of animals (i. e. mammals 

 and Peripatus). 



A point in the development of Peripatus imthurni, to 

 which I have not yet alluded, and which I am unable to 

 explain satisfactorily, is what may be termed the inversion of 

 the layers. 



An inspection of the figures will at once show that the 

 epidermis of the young Peripatus is apparently formed from 

 the inner layer of cells, and conversely, that the hypoblast is 

 formed from the cells that are, morphologically speaking, part 

 of the outside layer of the embryo. I have not been able to 

 find an explanation of this inversion, though I have made great 

 efforts to do so. I think, perhaps, that the so-called amnion 

 may be concerned in its explanation ; until, however, I am able 

 to procure more material, I cannot offer any definite explana- 

 tion of this curious phenomenon. 



It may be interesting to note the differences between the 

 adult Peripati, since they differ so immensely in their 

 development. 



The species of Peripatus about whose anatomy anything is 

 known seem to fall into three groups : 



(1) The New Zealand species (P. nov^e-zealandi^e), which 

 stands by itself. 



(2) The Cape species, three in number (P. capensis, P. 

 brevis, and P. Balfouri). 



(3) The South American species (P. Edwardsii, P. tor- 

 quatus, and P. imthurni). 



The only really important anatomical difference between the 

 groups 2 and 3 is that in the South American species there is 

 present between the ovary and the receptaculum seminis 

 another closed thin-walled vesicle (" ovarian funnel" of Gaf- 

 fron (1), receptaculum ovorum, Kennel (3)), which Sedgwick 



