DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 671 
cod, °06; grey gurnard, 055, and oil-globule, ‘0116; lemon dab, 053; flounder, -038 ; 
common dab, ‘033; skulpin, ‘025 to 030; sprat, ‘044 in long diameter, ‘039 in short 
diameter ; sole, 045. 
Tue Eac-CapsuLrk, WITH REMARKS ON THE REPRODUCTIVE ORGANS AND 
PERIOD OF SPAWNING. 
Few points in the constitution of the ovum afford more matter for controversy than 
the origin and significance of the external protective membrane. 
The twofold division of egg-membranes, due to Prof. E. van Brnepren (No. 24, 
pp- 228-30), and founded upon their derivation, is both natural and convenient, viz., (1) 
membranes differentiated from the cortex of the egg-mass itself; (2) membranes formed 
ab extra by the cells of the ovarian follicle. It is generally agreed that the egg-capsule 
of Teleostean ova belongs to the first division. CUNNINGHAM, however, does not adopt 
this view, and the “ vitelline membrane” of his earlier papers he now considers to 
be an extra-vitelline product—developed by the cells of the follicular epithelium 
(No. 47). Other protective structures may lie outside the egg-capsule proper, such as 
the mucous layer in Perca fluviatilis, the gelatinous matter surrounding the floating ova 
of Lophius piscatorius, and others, but they are probably ovarian, oviducal, or other 
secretions, and do not belong to the ovum proper. Further, it seems most in accord 
variously 

with present results to regard the external capsule as a single membrane 
styled Eikapsel (MULiEr, His, &c.), Eihaut (Kuprrer), Chorion (LEREBOULLET), Ectosac 
(OwEN), outer yelk-sac (Ransom), and zona radiata (WALDEYER). G. Brook, again, 
describes in Trachinus a thin membrane (his vitelline membrane) outside the zona. 
Such has not been seen in any of our pelagic eggs. It is generally hyaline, tough, and 
slightly resilient, and varies in thickness in different species—thus approximately in 
Anarrhichas lupus, it is 00143 to 00162 in. Gadus merlangus, it 1s 000310 in. 
Gastrosteus spinachia, ,, “0015 4 Pleuronectes flesus, rh 000125 ,, 
Gadus morrhua, y 000312 ,, | A limanda, ,, 000104 ,, 
» eaeglefinus, “ 000440 |) = Trigla gurnardus, f 000333 |, 
In pelagic ova it is so exceedingly thin and translucent that the developmental 
changes in the germ are visible through the capsule,* yet in demersal ova it is not only 
denser, but presents in many species marked structural features, such as projecting knobs, 
filamentous processes, reticulations, and the like, all of which, however, must be looked 
upon merely as modifications of the single capsular membrane—the zona radiata. It is 
very thin and transparent in the sprat, the egg of which generally shrivels when put in 
spirit. The zona usually presents laminze, which Sars observed and counted in Gadus 
morrhua ; but such does not imply the existence of separate layers, for chitinous structures 
of this kind often show a stratified condition. Ryprr could only make out the lamin 

*In undeveloped and dying eggs the growing opacity of the vitelline mass is readily seen. This opacity of the 
egg-contents ANDRE wrongly attributes to the capsule itself, which he says becomes opaque (No. 4, p. 197). 
