12 Moll. 
MOLLUSCA. 
Namnidce)f and its formation in a coecal appendage of the penis, termed 
by 0. Semper “Kalksack” [sac containing calcareous particles], and 
essentially identical with the “ flagellum^” by G. Pfeffer, JB. mal. Ges. 
V. pp. 264-271. The spermatophore of several species of Nanina and 
Macrochlamys described ; id., Arch. f. Nat. xliv. pp. 424-426, pi. xiii. 
figs. 7-14. 
A paper on spermatogenesis in the Pulmonata, by Duval, Rev. Montp. 
vii. pp. 277-302 [not seen by the Recorder]. 
6. Embryology. 
The development of Anodonta after leaving the gills of the parent 
has been studied by Max Braun and Carl Schieruolz, and the con- 
siderable gap hitherto existing in our knowledge of its young state filled 
up for the greater part. The larva fixes itself to the fins, gills, or bar- 
bels of living fishes, grasping the skin by the two strong hooks situated 
at the margins of the embryonal shell. The byssal thread serves, accord- 
ing to Schierholz, not only as a feeler, but also for interlacing several 
individuals together, and bringing all to the fish when one of them has 
grasped it. The bundles of bristles are probably sensitive organs. The 
young animal is then enclosed in a cyst, formed by a growth of the fish's 
skin at the infested spot, passing therein, according to Braun, 71-73 days. 
Du^jing this time, the young shell does not grow in size, but the whole 
organization of the animal, including the histological composition of the 
mantle, is changed. Both observers agree in the statement that the foot, 
intestine, ganglia, and gills are definitively formed during this stage, 
at which the genital organs have not made their appearance. Schierholz, 
differing from Braun, says that the first traces of these organs can be 
distinguished in the embryo in the gills of the parent, and that the two 
adductor muscles are found in the enclosed stage, the larva having only 
one central adductor ; but Braun avers that the latter disappears and the 
anterior and posterior are both newly formed. Schierholz maintains that 
the old central adductor is transformed into the anterior, and that only 
the posterior is newly formed ; the fore and hind parts of the embryo, 
according to him, have been mistaken by former observers, the mouth and 
vent being situated far backwards in the embryo. If the young animal 
is fixed to a fin ray, this weakened and thinned ; Braun thinks that the 
Mollusk draws a supply of calcareous matter from it, which is not ad- 
mitted by Schierholz. The latter describes also the embryonal develop- 
ment in the egg, and points out how that part of the yelk in which the 
multiplication of cells is the more energetic is prevented from touching 
the egg-shell by something like a directive vesicle, as long as the embryo 
floats in the egg. He also states that the young of Anodonta grows much 
more rapidly than that of Unio, the former reaching at the end of the 
first year the size of about 15, of the second 22, and of the third 26 mm., 
whereas Unio only reaches about 7, 12, and 14 mm. The observed 
species of Anodonta left the fish in April or May, those of Unio in July 
or August. O. Schierholz, “ Zur Entwicklungsgeschichte der Teich- und 
Fluss-muschol,” Berlin : 1378, 71 pp. 3 pis. ; a short abstract in Z. wiss. 
