110 BULLETIN OF THE 
posed of a slightly opaque greenish centre, vt, the diameter of which is 
two-thirds that of the egg-capsule, and a superficial transparent layer ¢, 
which may bea thickened envelope, part or the whole of which later 
becomes a vitelline membrane. Both these elements of the ova are 
affected by segmentation. 
The transparent plasmic envelope of the vitellus of Ophiopholis is 
thought to be identical with a similar layer described by others in star- 
fishes and sea-urchins. Selenka,* for example, has described a similar 
layer in Toxopneustes variegatus, and the question of the origin and fate 
of the vitelline membrane (?) has been discussed by Giard, + Fol, ¢ 
Perez § and Selenka.|| The discussion of the intricate complications of 
the question which the origin and fate of the cortical layer of the Echino- 
derm egg necessitate, must be passed over at present, as most of the 
phenomena considered by the above-mentioned authors antedate a stage 
of the Echinoderm egg corresponding with the youngest Ophiopholis 
which I have studied. The observations here recorded are supposed to 
have a value in indicating the existence of the cortical transparent layer 
in the Ophiurans where, possibly with the exception of Amphiura, it has 
been overlooked by other embryologists. 
The outer or superficial layer of the yolk is believed to be the same as 
the “‘Structurlosen geblichen Hiille,” described by Metschnikoff (op. cit. 
p. 14), in Amphiura. The same layer is thought to be figured by him in 
Pl. III. figs. 3-6, mv. as the “ Dotterhaut.” 
While the outer membrane of the Amphiura egg is conspicuous in 
Metschnikoff’s figures of the youngest eggs, in older stages it suddenly 
disappears. The same thing occurs in the capsule of the Ophiopholis 
ego, which leads me to suspect that they are the same structures. 
oo? 
According to Apostolides {J a part of the protoplasm seems to condense 
* Beobachtungen iiber die Befruchtung und Theilung des Eies von Toropneus- 
tes variegatus. Sitzungsb. d. phys.-med. Gesells. z. Erlangen. X. pp. 1-7. Zoologische 
Studien. I. Befruchtung des Eies von Toxopneustes variegatus. Leipzig, 1878. 
t Compt. Rend. LXXXIV.7 (Trans.) Ann. Mag. Nat. Hist. [4] XIX. 118, pp. 454- 
436. 
t Compt. Rend. LXXXIV. No. 14; id. LXXXV. No. 4; id. No. 14. 
§ Op. cit. 
\| Op. cit. The external transparent region mentioned above may correspond 
with the “superficial hyaline membrane” described by Fol (Ann. Mag. Nat. 
Hist. [4] XX.) over the vitellus of the starfish ovum. See also Perez, Sur la 
Fécundation de ’Giuf chez l’Oursin. Compt. Rend. Acad. Sci., LXXXIV. p. 620; 
LXXXV. p. 853. Ann. Mag. Nat. Hist. [4] XX. pp. 156-158. 
I Cp. cit. 
