54 SUMMARY OP CURRENT RESEARCHES RELATING TO 



the hypothesis that the Myriopod secretes a material which under 

 certain conditions is decomposed and gives rise to hydrocyanic acid 

 as one of its products ; the hypothesis has been entirely confirmed. 

 By the use of various reagents a body has been shown to exist which 

 is broken up by water and yields HCy among the products of its 

 decomposition. Further, it seems probable that the species in question 

 contains another substance which acts as a ferment ; this may perhaps 

 be isolated by future experiments. 



Embryology of the Chilopoda.* — N. Sograff's account of the 

 earlier stages of the development of the egg of the Chilopoda is 

 derived from a study of two species of Geophilus (^ferrugineus and 

 proximus, Koch) whose ova are better than those of Litlidbius for the 

 purpose. 



The ova of G. ferrugineus have a fine ruby-red colour and are 

 almost perfectly transparent ; they are probably the same as those 

 figured by Metschnikofi" in his researches. Parthenogenesis appears 

 to occur in this case, as males were not found at the end of April, but 

 only females, of which three had empty receptacula seminis, whilst at 

 the beginning of June eggs were produced by some of these females 

 and commenced their development. 



While in the oviduct the egg is enveloped in a transparent coat 

 which appears to consist of the united chorion and yolk-membrane, 

 for these structures can be distinguished in young ovarian ova. At 

 this stage the egg is filled with yolk, hiding the germinal vesicle and 

 yolk-nucleus ; but on one occasion a nucleated mass of protoplasm 

 — the nucleus being spindle-shaped, and exhibiting division of its 

 chromatin into two groups of rods — was found in the centre, probably 

 derived from the germinal vesicle. The nucleus and protoplasm 

 divide into a considerable number of portions ; the central cleavage- 

 masses are round or polygonal, the peripheral ones stellate. Yolk- 

 cleavage now takes place, the yolk breaking up into pyramidal masses, 

 as in the Decapoda, these masses carrying portions of protoplasm upon 

 their apices; the segmentation is not dichotomous; the number of 

 pyramids was always the same and the only difference between the 

 young and the perfect pyramid consists in an indefiniteness of outline 

 in the apex of the former. The simultaneous origin of these masses 

 is not an impossible circumstance, and is explained by the action of 

 the central protoplasm in drawing in to itself the superincumbent 

 yolk. The protoplasm-masses of the yolk now sink into the pyramids 

 which form the primary endoderm, and the central protoplasm-masses 

 come to the surface of the ovum and form the primary ectoderm. 

 In the Chilognatha, judging from Polydesmus, the method of formation 

 of the blastoderm more resembles that of the Crustacea and Arachnida ; 

 the yolk-cleavage appears to have been correctly described by Metsch- 

 nikoff. The blastoderm of Geophilus consists at first of large, pale, 

 very thin cells, dividing very rapidly, so as to form, in the course of 

 24 hours, a number of very small cells, which are, however, smaller on 

 one side of the ovum than on the other ; on this side the primitive 



* Zool. Anzcig., v. (1882) pp. 582-5. 



