88 Mr. E. E. Prince on Oleaginous Spheres in the 



situations in different species, occurring within the yolk mass 

 or outside it, in the perivitelline space, or rather in a fossa or 

 pocket indenting the surface of the yolk. Examples of the 

 latter condition are afforded by the Gadoid ovum studied by 

 Hackel, and by J\IofeUa musteia, Loj^ki'us 2J'iscatoriuSj Molva 

 vulgaris, and other forms. Instead of being seated, however, 

 in a depression or pocket lined by the cortical protoplasm of 

 the vitellus, the large vesicles may lie within this protoplasmic 

 layer, or rather in the albuminoid matrix of the yolk. 



In Gastrosteus, Liparis, Coitus, Cydopterus, and other 

 demersal eggs the globules, which are very numerous, and 

 collect together in a large group at the vegetal pole, are thus 

 surrounded by yolk substance, which, however, has sufficient 

 fluidity to permit free movement, and the mass of vesicles 

 may be made to traverse all j)arts of the inner surface of the 

 yolk cortex, by turning the e.^g about in various directions. 

 An interesting American pelagic &^^, Temnodon saltator, 

 which exhibits a single globule only, is in like manner im- 

 bedded, and has apparently shifted to a position immediately 

 beneath the germinal disc in the figures given by Agassiz 

 and Whitman*. Professor M'Intosh has proved that the 

 globule in Trigla gurnardus does not occupy a position in the 

 perivitelline space, as some observers have stated, but freely 

 moves through the deutoplasmic mass. 



1 hough thus capable of transference from one region of the 

 yolk to another, the normal position always is distal to the 

 animal pole, and to this upper (vegetal) segment the globules 

 invariably return when the rotated t^^ comes to rest. These 

 vesicles in some ova seem to have less freedom of movement, 

 and appear to be imprisoned by the surrounding matrix. 



ThusE. Van Beneden speaks as follows of the ovum examined 

 by him : — " The animal pole was always directed downwards, 

 the vegetative pole upwards. I ascertained that in my eggs 

 the position of the oil-drop was quite constant. It is always 

 placed eccentrically, and invariably occupies a position in tFie 

 vegetative hemisphere, but is immersed in the albuminoid 

 substance which surrounds it on all sides. I have in vain 

 endeavoured to explain to myself this fact by some peculiarity 

 of structure in the protoplasm. I entirely failed to discover 

 any trace of filaments connecting the oil-drop either with the 

 surface of the vitellus, or with the germinal disc "f. It may 

 be noted that the pseudopodial threads here referred to have 

 been seen in Gaatrosteus spinachia J, G, aculeatus, G. pun- 



* ' Studies from Newport Mar. Lab. — XVI./ plate iv. figs. 1 and 2. 

 t E. Van Beneden, Quart. Jouru. Micr. Sci. vol. xviii. p. 44. 

 I Ann. & Mag. Nat. Hist. 1885, vol. xvi. p. 492. 



