MR. .T. F. BULBAR, OFT THE DEVELOPMENT 
50G 
Development of Oniscus Murarius,” namely, by heating them in water and then 
hardening them, first in bichromate of potash and then in alcohol, beginning with 
70 per cent., and gradually increasing the strength to absolute. Some of the speci- 
mens were embedded in a mixture of solid paraffin and ordinary paraffin oil,* * * § others in 
spermaceti and castor oil. In all cases the sections were stained with Kleinenberg’s 
liaematoxylin and mounted in Canada balsam. I found that the most convenient way 
to heat the eggs was to put them in a test tube with a little sea water, and hold this 
in a vessel of boiling water for a few minutes. 
The eggs are carried by the parent in a large brood-pouch until the young are able 
to swim as among the lion-parasitic Isopoda. I have found both the adults t and 
young in all stages of development from the beginning of January to the end of June, 
so breeding probably continues all the year round. 
The eggs when first laid are surrounded by a single somewhat tough structureless 
membrane (fig. 1, O.M.). 
I have not been able to observe the first stages of segmentation ; the earliest which 
I have to describe is that in which a circular patch of cells has appeared on the egg 
(fig. 1). The cells have already become rather numerous, so that a diameter of the 
blastoderm passes through about twenty. The cells (figs. 1 and 2) are of considerable 
size, and contain very large granular nuclei. Seen from the surface, they appear of 
much the same size in all parts of the blastoderm ; but a section shows that in the 
central part they are polygonal in shape and more than one layer thick, while towards 
the circumference they form only a single layer, and at the extreme edge become 
flattened. Extending from the edges of the blastoderm over the yolk is an exceedingly 
thin granular layer. 
The cells increase in number and decrease in size, the blastoderm spreads more and 
more over the yolk, and the central thickening, or Keimstreif, losing its circular outline, 
begins to shape itself into the form of the future embryo. In fig. 2a the head end 
of the embryo is already distinct, and the two frontal lobes (Fr.) have appeared, 
though as yet there are no traces of appendages. The posterior part of the embryo 
is still quite indistinct. Whether the blastoderm spreads by the division of the 
cells of the circular patch described above as in Oniscus J and My sis, or by the separa- 
tion of fresh protoplasm from the food-yolk as in AseHus ,§ 1 have not been able to 
determine. The Keimstreif becomes more and more elongated, and soon attains the 
stage shown in fig. 3. In addition to the original membrane, a second very thin one 
has now appeared, which is for the most part closely applied to the surface of the 
yolk, but at certain points is slightly separated from it and is easily seen. It is not 
cellular in structure. 
* The kind used for lamps. 
f “ Gen. organs of Parasitic Isopoda,” ‘Jour. Anat. and Physiol.,’ yoI. xi., p, 118. 
+ Bobeetzky, Inc . cit . 
§ Van Beneden, Bull. Acad. Roy. Belg\, t. xxviii, 
