3^ SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 89 



an indirect evidence of their affinity. The chief difference seems to 

 be their biology : the Oxyurata are parasites from the first stage to the 

 last— no free-living larvae seem to exist among them ; there is no clear 

 metamorphosis in this group. A larva just hatched is always readily 

 recognized as a young oxyurid, generally very similar to the adult 

 stage except for its size and genital organs. It could be said that the 

 Oxyurata are modified by parasitism from the beginning to the end 

 of their lives, contrary to which the parasitic Anguillulata always con- 

 serve some free-living stage and their larvae are similar to the free- 

 living forms of the order. 



Another distinction could be found in the physiology of both 

 orders. As was said, the general character of the free-living Anguil- 

 lulata is their impermeable thick cuticle ; it is fully conserved and 

 even strengthened in the not numerous intestinal parasites belonging 

 to the order, such as Cephalobium. The musculature is strong and 

 the movement quick and alert, the body cavity is generally filled up 

 by different cells and conserved only as fine clefts between them. 

 Quite otherwise is the general constitution of the Oxyurata. The 

 cuticle is fine, impermeable enough for organic bodies, but not for 

 water, which easily passes through it. The body cavity is well devel- 

 oped and filled with a fluid content. The body is swollen and its 

 walls are stretched from the inside by the turgor thus arising ; it can 

 be easily proved by damaging the body walls, the body cavity fluid, 

 together with the inner organs, being then ejected with force. The 

 semipermeability of the cuticle can easily be demonstrated by plac- 

 ing these nematodes in solutions of different osmotic strengths. The 

 solutions with higher osmotic pressure will produce a general 

 squeezing of the body and finally even the separation of the cuticle 

 and hypodermis, and the further squeezing of the body inside the 

 cuticle, the general picture being then very like that of plasmo- 

 lyzed plant cells. The solutions with higher osmotic pressure will 

 produce a general swelling and tension of the body and sometimes 

 even its bursting. The musculature of most of the Oxyurata is 

 meromyarian and platymyarian, therefore very weak, and the move- 

 ments are slow and clumsy. 



This order seems to be very natural. The writer does not under- 

 stand very well why it was separated in several independent families 

 by Baylis and Daubney (1926), but probably it was on purely taxo- 

 nomic grounds ; the elimination of several genera into the Rhabdi- 

 asata (i.e., Anguillulata in our classification) by Travassos (1930) 

 seems also to be inadequate. The more common way of uniting 

 them into one order, as was originally proposed by Railliet and 



