738 SUMMARY OF CURRENT RESEARCHES RELATING TO 



The author is careful to point out that, in this comparison, he is 

 epeakinf' only of resemblances, and does not suppose that there are close 

 relations between the Nematode and the Insect. The pai-allelism 

 in life-history is due to similarity in external conditions. Both forms 

 lead a parasitic life, and both have adapted themselves to its require- 

 ments. 



The author deals in detail with the structure of the male, of the 

 female, with the embryonic and the post-embryonic development. All 

 the forms, except the pregnant females, are of microscopic size ; the 

 free-living larvae were found in suflScient numbers in the earth, sticking 

 to the root-fibres. The best media for investigations were found to be a 

 1/2 per cent, salt solution, or egg-albumen ; to stop their movements the 

 animals were slightly warmed over a spirit-lamp, and were thus extended 

 though not killed. 



Integument of Heterodera Schachtii.* — M. J. Chatin has investi- 

 gated the structure of the integument of Heterodera Schachtii, and the 

 modifications which it undergoes in fertilized females. In a young adult 

 female the integument is formed of a cuticle with a hypodermis, which 

 invests the musculature of the body. The superficial layer of the cuticle 

 is striated, and the deeper layer is fibrillar. The former is transparent, 

 refractive, and capable of resisting most chemical agents, and above all 

 alkalies ; its elegant circular striae are due to the presence of ringlike 

 elevations, which are separated by fine grooves. The hypodermis is 

 formed of a granular layer in which there are well-marked but not very 

 numerous nuclei. Immediately below it there are thick layers of muscular 

 tissue. The first change which is observed as a result of fertilization is 

 a diminution in the number of the nuclei of the hypodermis, which at the 

 same time becomes clearer. As the female increases rapidly in size, the 

 muscular layers become more and more delicate, and undergo a sort of 

 delamination. Later on their retrograde change is marked by others 

 which obtain in the hypodermis. In that layer the number of nuclei 

 increases remarkably, and with the proliferation which obtains there is 

 also to be noted the appearance of viscous and refractive droplets, which 

 collect at the surface of the cuticle. This exudation does not escape by 

 cutaneous pores, of which there seem to be none, but by local ruptures 

 of the cuticle, which yields to the enormous growth of the body distended 

 by ova. 



The muscular layers disappear, sometimes a vestige being left in the 

 form of a delicate band attached to the hypodermis, which becomes very 

 delicate, and tends to fuse with the cuticle. If the ova are set at liberty 

 directly, the cuticle breaks at several points and follows the other tissues 

 of the integument in their fate of disintegration. 



The facts just detailed show that those histologists have erred who 

 have refused to distinguish sharply the integument from the musculature. 

 Some of the changes that are undergone recall the phenomena of histo- 

 lysis in other Invertebrates. The brown cyst which is sometimes formed 

 for the eggs, being constituted by the exsudation from the hypodermis, 

 is neither a new pathological form nor an induration of the integument 

 of the worm. As a measure of prophylaxis it would be well to look for 

 mothers with, disorganized integuments. 



* Comptes Eendus, cvii. (1888) pp. 139-41. 



