1180 General Notes. [ November, 
descendants of the cleavage-cells. Leuckart holds that these are 
he germ-cells of the next generation, and that their number 
remains the same when the sporocyst stage is reached. Thomas 
also regards these as germ-cells, but thinks that their number is 
augmented by germ-cells derived from the epithelial layer which 
lines the cavity of the sporocyst. According to Leuckart then 
the germ-cells are ready formed from the outset; but according 
to Thomas some are ready formed while others have an epithelial 
origin. : 
Biehringer has settled definitely that germ-cells do arise in the 
epithelium, but leaves the question of a two fold origin of germ- 
cells still open, not having been able to trace the history of the 
cells which fill the interior of the embryo. 
A cell in any portion of the epithelium divides into two cells, 
the plane of division cutting the 
axis of the sporocyst at right 
angles, as in Fig. 1g. Further 
division gives four, eight cells, 
&c., ending in the formation ofa 
morula-like mass which escapes 
from the epithelial layer into the 
central cavity, and here completes 
its development. This mode 
THE DEVELOPMENT OF THE JAWs OF BRANCHIOBDELLA AND A 
METHOD OF ISOLATING THEM.!—The jaws, of which there are to, 
one dorsal and one ventral, are formed on small papilla as cube 
ular secretions. The papille represent slightly thickened areas 
of the epithelium lining the cesophagus. The jaws then af 
merely thickened portions of the general cuticula which covers 
the whole of the external surface of the worm as well as the epi- 
thelium of the cesophagus. . f 
The five or more denticles on the lateral and posterior ae 
the jaw are each the product of a single cell which 1s slightly 
longer than the other cells of the papilla. i icular 
In order to isolate the jaws and with them the entire cuticu 
mantle, it is only necessary to leave a Branchiobdella in an ac 
watch-glass until it has dried, and then cover it with water. Z 
cuticula will expand to its original size, leaving the she 
animal inclosed as in a sack. The sack can then be cut throni 
the middle and the animal easily removed by slight pressu"? ©, 
the aid of a small brush. The jaws will then be seen coher 
with the cesophageal portion of the cuticular sack. ye 
‘Walter Voigt. Semper’s Arbeiten, VIL, pp. 47 and 54-55, 1884- 
