Mr. Bastian on the Anatomy and Physiology of Nematoids. 199 



of the parasitic species, he thinks considerable light is thrown upon 

 the function of the " water-vascular " system. He says, " Here we 

 have undoubtedly to deal with an excretory glandular apparatus. 

 No one could for a moment regard these structures as at all analo- 

 gous to vessels destined alternately to receive and discharge an ex- 

 ternal fluid medium. I believe that in the Trematoda and Tceniada 

 also, where similar though often more developed systems exist, their 

 function is in like manner one of a purely eliminatory kind ; and 1 

 therefore cannot but look upon the name of ' water-vascular ' appa- 

 ratus as a singularly inappropriate appellation for this system of 

 vessels." 



Other very peculiar transverse vessels exist in the deep integu- 

 mental layer of Ascaris megalocephala and A. lumbricoides, mostly 

 running in pairs from median line to median line, and, strangely 

 enough, being about twice as numerous on the right as on the left 

 side of the body. 



The author believes that in the Nematoids but little provision 

 exists for the oxidating portion of the process of respiration, and 

 thinks that this deficiency may be compensated by a greatly increased 

 activity of glandular eliminating organs. Considering the conditions 

 under whose influence so many of the parasitic forms pass their 

 existence, we can easily imagine that the presence of any organs for 

 effecting an oxidation of their tissues would not only be useless, but 

 actually baneful. Glandular organs exist in the greatest abundance 

 in all Nematoids, and raanj' of these are excretory organs. In those 

 species in which no modification of the ventral excretory apparatus 

 is met with, the author has found a very large number of channels 

 running through the chitinous portion of the integument, so as to 

 bring its deep cellular layer into communication with the exterior. 

 These pores are, he believes, complementary respiratory organs, and 

 their development is always in an inverse proportion to that of the 

 other excretory organs. Thus amongst the free Nematoids he has 

 found them most numerous in Dorylaimus stagnalis and Leptoso- 

 matum figuratum — species in which the ventral excretory apparatus 

 is entirely absent. The same arrangement is met with in the Tri- 

 chocephali and Trichosomata, in which these integumental channels 

 attain their maximum development. The gradually widening longi- 

 tudinal band long known to exist in the Trichocephali is due to the 

 presence of thousands of these channels in connexion with a glandular 

 development of the deep integumental layer beneath. 



Many interesting facts are brought forward concerning the " tena- 

 city of life " of some of the free Nematoids, and their power of re- 

 covery after prolonged periods of desiccation. This has been long 

 known as one of the characteristics of Tylenchus tritici*, but the 

 author has found it common only to the species of four land and 

 freshwater genera — Tylenchus, Plectus, Aphelenchus, and Cephalo- 

 bus. The remainder of the free Nematoids are remarkably frail, and 

 incapable of recovering even after the shortest periods of desiccation. 



* Vibrio tritici of older writers. 



