i889.] Embryology. 829 
so clear and fine as when one uses the best haematoxylin crystals. 
This last solution must be diluted with alcohol saturated with alum if 
over-staining is to be avoided. And if either of the preceding dyes, 
Kleinenberg's or Delafield's, is used, it should be diluted until the 
solution is not too opaque to read through if placed over print in a 
glass dish to the depth of one-quarter inch. In this the embryos may 
be left sixteen to twenty-four hours, or until they are dark purple. 
The embryos may then be embedded in paraffine and sectioned 
lengthwise, and some in a vertical and others in a horizontal plane, as 
well as transversely and mounted serially in the usual way with the aid 
of a fixative. This gives a complete view of the organization of the 
larvai, as well as a good opportunity to study the karyokinetic displays 
thus rendered visible by the haematoxylin. The chromatin threads 
are deeply stained by the dye and come out very sharply, and contrast 
with the rest of the substance of the cells. 
The connective tissue which forms the cores of the branchial plumes 
is very interesting at this and later stages, as its cells are vesicular or 
form a meshwork tensely filled with fluid, which forms a supporting 
structure similar in function to the vesicular tissue of the axial noto- 
chord. 
Around the connective tissue cores of the branchial plumes, and 
overlaid by the epidermis, the branchial vessels form a meshwork 
which is thus brought close to the surface for purposes of respiration. 
The tips of the tails of more advanced larvae are attenuated for a 
short distance into an upwardly bent point which recalls the opisthure 
of some larval fishes^ as well as the upward flexure of the notochord in 
those types where the phenomena of heterocercy are almost universal. 
This fact indicates that some of the types ancestral to the lower 
Batrachia may have been heterocercal. 
The lateral sense organs in just-hatched larvae are also conspicuous, 
and form two rows along the sides of the trunk and but one over the 
sides of the tail. Over the sides and top of the head they are more 
crowded together and never elongated as in Amia. On the inferior 
side of the head the rows of sense organs follow the direction of the 
now-closed branchial clefts ; three curved rows of them may be made 
out on either side of the median line. In surface vie^vs a minute 
circular patch of pigment marks each sense organ, around which there 
IS an annular colorless ring. — John A. Ryder. 
