FEES NEMATOTDS. 
173 
should be more or less covered with sand. His explanation of 
this fact was, that the access of air exercised a prejudicial in- 
fluence upon the delicate tissues of these animals. The fact 
is quite in accordance with my own observations ; and, as regards 
explanation, I am able to offer none more satisfactory than that 
advanced by Spallanzani. From numerous experiments, I 
have ascertained that the power of recovery after desiccation, 
possessed by the Nematoids found in moss and lichen, is most 
wonderfully curtailed if animals singly are placed upon a 
clean slip of glass, and allowed to become dry when thus 
freely exposed to the air. For instance, as a rule, these same 
Nematoids of moss and lichen, which showed such a marvellous 
tenacity of life in the experiments of Doyere and Gfavarret, 
rarely recovered at all after an exposure of forty-eight or 
even thirty-six hours on a glass slip. So far as I have seen, 
young specimeDS are certainly not capable of resisting expo- 
sure better than or even as well as adults, although the reverse is 
notably the case with Tylenchus tritici. But with animals be- 
longing to the genera Chromadora, Enoplus, Monhystera, 
Leptosomatum, Mononchus, Dorylaimus, and many others, the 
results have been very different and almost uniform. I have 
never succeeded in restoring any of these animals after they 
have remained dry and motionless on glass for two minutes ; 
many would not recover after one minute of such exposure, and 
with Chromadora communis, one of the most abundantly 
represented species of our tide pools, I have rarely been able to 
revive specimens after even half a minute’s exposure, dating 
from the time of the cessation of movement in the drying 
animal, as seen under the microscope. 
It seems to me that the increased tenacity of life exhibited 
by the members of the four genera Tylenchus, Aphelenchus, 
Plectus and Cephalohus, is partly connected with the power 
they possess of retaining their tissues in a moist condition for 
a longer time than the others, owing to the comparative or 
even total absence in them of the integumental pores which 
appear to be present in most of the other species of free Nema- 
toids. The fact that such pores cannot be discovered .. in any 
of the members of these genera is pretty certain, and these 
differ from other free Nematoids also by the possession of pecu- 
liar lateral vessels, and a modified structure of the ventral 
excretory gland, whose dnct seems very much narrower and 
more rigid, than when it occurs in species which have not the 
same tenacity of life (figs. 5 and 7). 
Before concluding these remarks on the Free Nematoids, I 
would point out that although, in a zoological sense, these 
animals are to be considered as quite distinct from the parasitic 
Nematoids, still we see, on examining more closely, certain 
