408 Royal Society : — 



membrane), and in Glomeris of the epithelial layer only, is in the 

 Plialangidse, and perhaps all the Arachnida, formed only by the 

 outer membrane. Consequently, while in the insects the mature ovum 

 I)asse3 into the ovary through the neck of the follicle, in Myriapods 

 and the Arachnida it bursts through the epithelial layer, in tlie former 

 at its free, and in the latter at its attached end. 



If these characteristics are found eventually to hold good through- 

 out the Myriapods and Arachnida, the differences thus shown to 

 exist between these groups will be of great interest ; but it is too early 

 to generalize on the subject with much confidence. Moreover, it often 

 happens that one or a few epithelial cells are attached in Arachnida 

 to the inner side of the follicle-wall. This happens, however (as far 

 as my observations go), without any regularity, and the cells thus 

 present fulfil perhaps no important function in the formation of the 

 egg. The Crustacea appear to differ from the three preceding groups 

 in the fact that their eggs do not possess separate follicles. 



In the more advanced eggs of Glomeris, the macula of Wagner is 

 double, one being much smaller than the other. 



The ovary of lulus has been described by Newport ; the specimens 

 which he examined had, however, been submitted to the action of 

 spirits of wine, and were therefore altogether unsuitable for histolo- 

 gical examination. The egg-follicle did not contain any large vitelli- 

 genous bodies like those of Glomeris, nor could I see in it a vitelline 

 vesicle like that of Arthronomalus ; but it very generally contained, 

 when the yelk was beginning to darken, a patch resembling that 

 which appears to result from the small vitelline vesicle of Lithobius. 

 In both these genera the eggs in all stages of development are mixed 

 together without any regular arrangement. The macula appears to 

 be generally double, as in Glomeris. In the genus Polydesmus, 

 however, where, as in all Chilognaths, the eggs are arranged on a 

 double stroma, situated at the lower side of the ovary, the smaller 

 eggs are on the central parts of the stroma, and the more developed 

 ones lie towards the sides. In appearance the ova offer a great 

 contrast to those of lulus, and particularly of Glomeris, since the 

 margin of the yelk has all the appearance of being bounded by a 

 distinct membrane, though I am not convinced that this is really the 

 case. I have not yet made out in Polydesmus anything corresponding 

 to the "patch" o{ lulus. The macula appears to be always single. 

 It often contains vacuoles. 



The yelk of mature eggs consists, 1st, of globules about -^-^g-g-ths 

 of an inch in diameter ; 2ndly, of greenish bodies about y-ijyTjth in 

 diameter ; and 3rdly, of a clear, more or less viscid substance'. 

 By the month of October most of the females have laid their first 

 lot of eggs ; after which another set immediately begin to be deve- 

 loped. M. Fab re does not appear to have seen tiie spermatozoa 

 of Polydesmus. They are small elliptical bodies about -jj-j/oijth 

 of an incli in length, and containing a bright nucleus. M. Stein 

 appears to be the only naturalist who has hitherto described them 

 from personal observation, but he does not allude to the nucleus. 



In Lithobius, Cryptops, Geophilus, and Arthronomalus, the eggs 



