6 
W. E. AGAR. 
consist largely of spermatogonia of the earlier generations, 
arranged in many tubules as a definite lining epithelium. 
With the help of these three specimens, and of the little 
clumps of spermatogonia at the blind ends of the testis 
tubules of breeding males, it was easy to learn to recognise, 
both in the “ resting” and dividing states, the different cells 
of which the germinal epithelium is composed. The nuclei of 
these cells bear a close resemblance to those found in the 
salamander. Meves’ description of the different generations 
of cells in the testis of this animal could be applied closely to 
Lepidosiren. 
The spermatogonia are often divided into two classes — 
primary and secondary — but it is doubtful whether such a 
sharp distinction can be drawn in Lepidosiren. It is safer 
to speak of earlier and later generations of spermatogonia. 
Among the earlier generations are found many nuclei 
corresponding exactly with those described as primary 
spermatogonia by Meves. The chromatin in these, as in all 
the spermatogonia, is in the form of large irregular blocks 
connected by finer strands. What is particularly character- 
istic about these primary spermatogonia, however, is, that the 
chromatin is often obscured or almost entirely concealed by 
a diffusely staining substance filling the whole nucleus (PL 1, 
fig. 1). Meves notes this as a characteristic of the primary 
spermatogonia of the salamander, and considers that the sub- 
stance is a precipitate produced by the action of the fixative, 
since it is not found in the nuclei of the same cells in the 
centre of the sections. The impression gained from a study 
of Lepidosiren is, that the substance is most dense in nuclei 
which are undergoing a prolonged rest, and least abundant 
or altogether absent in those in a period of active multiplica- 
tion. At any rate, as soon as the prophase has definitely set 
in the nuclei are quite clear except for the sharply defined 
chromatin. 
The nuclei of these earlier generations of spermatogonia 
are frequently polymorphic — a characteristic of this class of 
nucleus in many animals. PI. 1, fig. 1 shows a moderately 
