ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 33 



perceive big movements. Theoretical conclusions must be carefully 

 corrected by experiment. The imperfection of visual sensation in some, 

 and the total absence of eyes in others, must be considered in association 

 with their mode of life. 



y. Prototracheata. 



Development of Peripatus Novae-Zealandiae.* — Miss L. Sheldon 

 commences by explaining that the want of completeness in her account 

 of the development of the New Zealand species of Peripatus is due to 

 the necessity of killing the gravid parents as soon as they reach England. 

 The ripe ovum of this species is large as compared with that of P. 

 capensis or P. edwardsii, the length of 1 • 5 mm. being due to the amount 

 of food-yolk with which the egg is charged. There is a thick tough 

 shell, and a thin and membranous vitelline membrane. The nucleus of 

 the egg before segmentation varies somewhat in position ; it may have a 

 'peculiar lobed form, and consist of three masses of deeply staining 

 material, between which is a portion of nuclear substance which stains 

 less deeply. The segmentation is like that of some other Arthropods, 

 and agrees with the mode lately described by Henking in certain 

 Pkalangicbe in the irregular arrangement, in young stages, of the nuclei 

 of the blastoderm ; but Miss Sheldon does not consider each yolk-seg- 

 ment as a single cell, for she found no relation between the yolk and 

 the nuclei. What differences obtained between eggs of the New Zealand 

 and Cape species are probably due to the presence of yolk in the former ; 

 in neither are there any cell-outlines, the protoplasm of both forming a 

 perfectly continuous reticulum in which the nuclei are imbedded. As 

 to the mode of development it might be said that the embryo is " formed 

 by a process of crystallizing out in situ from a mass of yolk, among 

 which is a protoplasmic reticulum containing nuclei." 



The embryo obtains its nutrition from the yolk contained within its 

 body, and from a peripheral layer of yolk in which are imbedded 

 numerous small, round, highly refractive bodies. This latter is a very 

 remarkable and unusual mode of embryonic nutrition, but its object is 

 evidently to supply the ectoderm with a constant source of nourishment. 

 A somewhat comparable arrangement has been described by Ganin in 

 Platygaster, and a somewhat similar result is brought about, though by 

 different means, in those insects which undergo an internal development, 

 and in which the embryo is completely imbedded in the yolk ; the pro- 

 cess in P. Novae-Zealandiae is simpler, fur nothing corresponding to the 

 amnion is present. It is, at any rate, clear that there are in Arthropods 

 various modes for the protection of the embryo and the nutrition of the 

 ectoderm, and that, though these differ very largely in their mode of 

 origin and structure, they resemble one another in their physiological 

 functions. 



The segmentation is on the centro-lecithal type; the protoplasm is 

 mainly at one pole of the egg, and in it nuclei arise, probably by the 

 division of the original segmentation nucleus. In the latest stage 

 observed the loose protoplasmic reticulum covered above half the 

 periphery of the egg. In the course of development the protoplasmic 

 area becomes more compact and flattens out, forming a plate-like mass 

 densely packed with nuclei ; at this time the embryo is a closed sac, the 



* Quart. Journ. Micr. Sci., xxviii. (1887) pp. 205-38 (4 pis.). 

 1888. D 



