EOSACETTS, LINCK (COMATTJLA EOSACEA OE LAMAECK). 
519 
lie in the groove of the calcareous joints. About the end of February or the beginning 
of March, the integument of the pinnules becomes slightly turgid ; and this turgescence 
increases till towards the end of May or the beginning of June, when the eggs are fully 
formed. 
The mature ovaries are short, entire, fusiform glands distending widely the inte- 
gument of the pinnules, and provided with a special aperture which perforates the 
distended skin on that side of the pinnule which is turned towards the end of the arm. 
The aperture is bounded by a somewhat thickened ring of apparently elastic tissue, 
which acts as an imperfect sphincter. Examining the ovary by compression shortly 
after it has begun to enlarge, the meshes of the stroma (Plate XXIII. fig. 1) are found 
to contain a clear mucilaginous protoplasm with minute ova in various early stages of 
development. Tracing the development of the ova, the formative fluid first becomes 
slightly opalescent, and a minute, highly refractive, lenticular body makes its appear- 
ance, which subsequently declares itself as the germinal spot. This body remains some 
time slowly enlarging without much further change. A delicate film now rises from 
one side of it, and this film gradually extends till the germinal spot appears to be 
attached to the inner wall of a spherical cell with perfectly transparent fluid contents, 
the germinal vesicle (Plate XXIII. fig. 2, a-c). The blastema in the neighbourhood of 
the germinal vesicle becomes slightly granular, and the granules accumulate so as to 
form a distinct granular layer round the cell. This layer, the nascent yelk, is shortly 
found to be invested by a delicate vitelline membrane ; but this membrane does not 
appear to originate from the germinal vesicle as a nucleus, as in the case of the 
latter from the germinal spot. The impression rather is that the surrounding fluid is 
influenced to a certain distance by the chemical forces acting in the germinal vesicle, 
and that a membrane is produced at the point of junction between the blastema so 
influenced and the general fluid contents of the ovary. The egg now increases in size 
without much further change in structure. The vitelline membrane rapidly expands 
(Plate XXIII. fig. 2, cl-o), and its contents become more dense, till at length it has 
attained a diameter of about ‘5 millimetre, and is entirely filled with a yelk-mass 
composed of oil-cells of the usual form. 
The ripe eggs are now discharged from the ovary ; they remain, however, for some 
time (in some cases three or four days) entangled in the loose stroma of the ovary, and 
hanging from the ovarian aperture like a bunch of grapes. 
The testis resembles the ovary in form and situation. A transparent mucus distends 
the integument of the pinnule. The fluid becomes opalescent, then granular, and 
finally the cavity becomes filled with amass of fusiform parent cells (Plate XXIII. fig. 4). 
The contents of these cells are at first perfectly transparent ; soon, however, they lose 
their transparency and become granular, and at length the cells are found to contain a 
progeny of ten or twelve minute spherical “ vesicles of evolution.” Bright refractive 
spots, the heads of the spermatozoa, three or four in number, appear in each of these 
secondary cells ; and finally, the walls of the parent cells and vesicles give way, and the 
