THE HISTOLOGY OF THE BLOOD OF LARVA OF ZEPIDOSIREN PARADOXA. 309 
in support of the supposition, that whatever may be the explanation of the outputting 
of the pseudopodium in the case of the leucocytes, the withdrawal and forward move- 
ment must be referred to the centrosome, with its sphere and radiations; and so far as 
the appearances go, they are in favour of the idea that the centrosome in this case also 
is the centre of a contractive force. 
In the conversion of the leucoblast into the leucocyte, the attraction sphere and 
aster are gradually unfolded as the cell body increases in size. The nucleus is at first 
central, but later assumes an eccentric position, while the sphere moves towards the 
centre of the cell. I would explain this in the same terms as I explained the rounding 
up of the erythrocyte, and the separation of its centrosomes. ‘The centrosome being 
here single, however, it comes to a position of equipoise in the centre of the protoplasm. 
My reading of the structure of the leucocyte is different from that of HzmEnnatn,* 
in so far as the radii seem to me to branch and join the general reticulum, which I 
believe (with the necessary reservations) probably represents an alveolar disposition of 
the protoplasm, but they act quite like his organic radii, in respect of the movement 
of the sphere. With regard to the form of the nucleus in relation to the movement of 
the sphere, my observations, so far as they go, seem to agree with his in matter of fact, 
but I have not followed out the point in such detail as to follow him into the domain of 
theory. 
EXPLANATION OF PLATES. 
The drawings were done, in everything but the very minute detail, by aid of the camera lucida (Abbé). 
The lenses employed were the 3 mm. and the 2 mm., both 1:4 numerical aperture, apochromatic 
| objectives of Zeiss, combined with the compensating oculars 8 or 12. The magnification indicated was 
ascertained by the stage micrometer. It is rather greater than the magnification given by the com- 
| binations used, the excess depending on the depression of inclined drawing-table beyond the visual distance. 
The coloured drawings were tinted with the same stains as used for staining the sections. The watery 
solutions of aniline dyes colour smooth Bristol board very delicately, and permit of a degree of verisimilitude 
difficult to attain with ordinary water-colours. 
The photographs were all taken with the 3 mm. 1°4 numerical aperture achromatic objective and No. 
4 projection eyepiece, at a distance which gave a magnification of 800, with the exception of fig. 37, in 
which the magnification is 1500. 
Puate I. 
Fig. 1. Section red blood corpuscle in plane parallel to surface of disc. x 1200 d. Compare photo- 
graph, Pl. IV. fig. 32, 
Fig. 2. Section of same in place at right angles to surface of disc. x 1200 d. Compare photograph, 
PEIY. fig. 33. 
Fig. 3. First stage of mitosis. Section passes through corpuscle in a plane vertical to its flat face. It 
is rounding up for division. Possible phase of single centrosome placed in a projection which has risen from 
centre of disc. x 1200 d. 
Fig. 4. Similar stage in larger corpuscle. Two centrosomes. x 1200 d. 
Fig. 5. Corpuscle with two independent centrosomes. x 1200 d. 
Fig. 6. Corpuscle with two centrosomes which have appeared separately as in last. x 800 d. 
* Loc cit. 
