THE HISTOLOGY OF THE BLOOD OF LARVA OF LEPIDOSIREN PARADOXA. 441 
characters they are identical with the later leucocytes. I may also remark that the 
general mesenchyme cells show in certain instances all the characters of these free cells 
in the blood, and that some even have definitely polymorphic nuclei. 
The next three stages may be described together, as there is no marked difference in 
the general characters of the blood. They are numbered 28, 29, and 30. 
The large ringed corpuscles have increased greatly in number, partly by active 
division, partly by new formation. That new formation is proceeding, I conclude, 
because both in the earlier stages and in those now in review there are appearances in 
the developing vessels under the mesepithelium over the mass of undifferentiated yolk 
cells which indicate the budding off of free elements from the superficial layer of 
smaller yolk-laden cells, and it seems to me probable that the opening out of the 
cardinal veins in the mesenchyme round the nephric ducts is also associated with the 
setting free of elements into the blood stream. ‘The enormous amount of yolk in all 
the cells at this stage, and the consequent large size of the cells (each cut through, in 
10 « sections, at least three times), make it very difficult, however, for one to satisfy 
one’s mind regarding this. 
Some of the yolk-laden blood corpuscles are at this stage of enormous dimensions. 
These giant corpuscles (fig. 6, Pl. VII.) are either round or oval. The round cells are 
about 60 « in diameter; the ring is very broad and distinct, enclosing the yolk grains 
and vacuolated protoplasm, from which it is sharply marked off. The large oval cells 
(fig. 7, Pl. I.) attain a length of 80 » to 90 4; I have met with individuals even more 
than 100 win length. In the smaller célls of earlier stages, as far as | can make out, 
the layer of superficial fibrillar protoplasm surrounds the greater part of the corpuscle, 
but in the elongated corpuscles it is massed at the ends, z.c. at the equator of the oval 
dise. The nucleus of all the corpuscles is of the ‘leucoblast’ type. It is spherical in 
the great majority of these large cells, but numbers have lobed or even multiple 
nuclei, and these often of very unequal size (fig. 11, Pl. I.). In the earlier stages of 
these three series under consideration mitotic figures are numerous; in the later 
they also occur, but less frequently, and the question arises whether the multiple 
nuclei arise by direct or indirect division. 
I have little doubt in referring to direct division certain cases in which the nucleus 
is a regularly shaped dumb-bell, and in explaining them as antecedent stages of cells 
with two equal nuclei lying side by side. In other cells of a smaller variety, to be 
mentioned immediately, the nucleus is irregularly lobed, and there are sometimes 
detached free portions, which must be produced by direct fragmentation. On the other 
hand, certain instances may be the result of indirect division of the nucleus without 
division of the yolk-laden body. The mitotic figures are not numerous enough to 
enable me to obtain a complete series without much labour, so that I have not followed 
this point out to a judgment. For the same reason I have been unable to determine 
the relation, if any, to the multiple and unequal condition of the nuclei, of a number of 
instances observed of irregular mitoses, some of which were multipolar. 
