1094 REPORT—1885. 
Laboratory. It was shown that the size of the nest depended upon the character 
of the materials employed and upon the number of female fishes resorting to a 
single nest; and it was pointed out that the dimensions (5-8 centimetres) named 
by Professor Mébius were often very much exceeded. If the fronds of the larger 
Algze (Fuci &c.) be chosen, the nest is pear-shaped or cylindrical, and of greater 
capacity (length 8-10 inches, and diameter, widest part, 5-6 inches) than when 
more minute seaweeds (Ceramium, Coralina, &c.) are selected. In the latter case 
the nest is more spherical, and 3-5 inches in diameter. Compactness is secured by 
binding threads upon the outside, which are often so disposed as to form a reticula- 
tion, the crossing cords enclosing lozenge-shaped spaces. The substance of the 
cords is a secretion which exudes from the epithelial cells of the sinuous urinary 
canals. The cells present (as transverse sections show), at the latter end of April 
and during May and June, a swollen appearance. The secretion is not merely a 
semi-solid plasm ; but, before reaching the spacious ureters at the external border 
of the kidney, assumes a marked funicular character. It is colourless, opalescent 
when freshly extruded, and of mucilaginous consistency. Mébius determined its 
nitrogenous composition: carmine stains it deeply, it becomes opaque in spirit, 
and after exposure to sea-water (for 2-3 days) it turns transparent grey or dirty 
white. It is thus a form of Mucin peculiarly modified, possessing extraordinary 
elasticity, and it is stored up in the urinary bladder. This structure is dispropor- 
tionately developed, pyriform, and describes a double curve, posterior to the cervix, 
before debouching behind the genital pore into a urino-genital sinus forming the 
posterior portion of the cloacal depression, into which the anus also opens. The 
weaving operation as seen in the tanks of the laboratory was referred to, and the 
structure of the cords then described. Each cord (‘0046-0051 in, in diameter) 
consists of several strands (‘0008—-00092 in. in diameter), and these constituent 
threads, again, are made up of fine homogeneous filaments adhering in parallel 
order, ‘he nest is so constructed by the male as to leave numerous irregular 
chambers, in each of which the female deposits some ova. ‘The ova are extremely 
ellipsoidal, disproportionately large, and the soft tenacious capsule assisted by an 
ovarian plasm causes them to adhere strongly together. If torn asunder facets or 
scars on the capsule mark the points of attachment to adjacent ova. The colour 
is a delicate pale green, which soon changes to the characteristic translucent amber 
tint. The hyaline capsule has a thickness of ‘0013 in., and is separable into 20 
to 30 lamelle. It is minutely punctured, the pits being arranged in parallel rows. 
A large mass of loosely aggregated oil globules occupies the vegetative pole. Two 
hours after fertilisation the cap is completed at the germinal pole, and sezmenta- 
tion presents the usual features, though it is comparatively slow. On the fourth 
day the nuclei of the periblast appear, and by the eighth day the embryonal thick- 
ening is well marked, epiboly having proceeded over two-thirds of the yelk surface. 
At the close of the same day the mesoblastic muscular plates are well-defined. 
Closure of the blastopore is effected on the twelfth day, and soon after Kupfer's 
vesicle is distinguishable. By the seventeenth day the heart assumes the campa- 
nulate shape; and the protovertebree are marked off from the otocystic region to 
the caudal plate. A heemal circulation is visible, though languid, on the nine- 
teenth day, and by simple lacunze hollowed out of the yelk-cortex spacious pas- 
sages are formed, and a yelk circulation, by the twentieth day, is in vigorous 
action. The young fish shows movement on the nineteenth day, and the first 
embryos emerge on the twenty-fifth day. The centrally-situated ova develop more 
slowly, many of these not hatching until the fortieth day. The water of the 
tanks varied from 41° F. in May to 50° or 51° F. early in June, and the general 
conditions of the laboratory being unusually favourable for the development of ova 
of marine fishes, the phenomena observed may be taken as almost normal. 
5. On the Reproduction of the Common Mussel (Mytilus edulis, L.) 
By Joan Witson. 
The common mussel is completely dicecious, and is peculiar in having the 
sexual elements developed in the mantle as well as in a wedge-shaped central 
