THe Hoa LousE 709 
as a true yolk chamber. This chamber remains small, there is no boundary 
between it arid the terminal thread, and its epithelium is composed of 
small nuclei between which cell boundaries are seldom seen. In young 
individuals the chamber contains only a few cells besides the epithelial 
nuclei (Plate LXVI, 4), while in older animals the cells are quite degener- 
ated and are broken up intoscattered fragments until finally only epithelial 
nuclei remain and these have migrated into theinterior of the chamber (Plate 
LXVI, 7). In every case Gross found a zone of transversely arranged 
epithelial cells behind the terminal chamber. Such a zone is characteristic 
of telotrophic egg tubes and has not been found in any other group having 
polytrophic egg tubes. In Haematopinus it is very short and in some 
cases is represented only by a row of much degenerated epithelial nuclei, 
distributed in the longitudinal direction of the egg tube. In the egg 
chamber (Plate LXVI, 9) there is a definite number and arrangement of 
nutritive cells. There are five of these, and the odd one lies in the apex, 
with the others in two successive rows immediately behind. The nuclei 
of all are irregular in outline. Such an arrangement was seen by Landois 
(1865 a:48) in Pediculus. The two hindmost nutritive cells push into 
the plasma of the egg, and there is seen a layer of dark-stained, bal!-like, 
little nuclei which are the nutritive substance introduced from the cell 
to the egg for the formation of the yolk. In the older individuals the 
follicle epithelium is clearly seen to be of two kinds. That surrounding 
the nutritive cells is thin and flat, having few nuclei and no distinct cell 
walls; while that surrounding the egg chamber is made up of deep cylindri- 
cal cells closely apposed on one another and containing cylindrical nuclei 
with an elongated nucleolus. The mitosis seen in the epithelium of 
younger stages has now given place to amitosis, and finally each cell 
contains two nuclei which lie behind each other in the longitudinal axis 
of the cell (Plate LX VI, 10). Gross has never seen cell division following 
the amitotic division of the nuclei, and in the light of more recent researches 
this nuclear division is to be regarded rather as a redistribution of nuclear 
material than as a true amitosis. Behind the egg cell the follicle ceils 
are hemmed in by a collection of dark nuclei similar to those behind the 
nutritive cells, and cell boundaries are wanting at this point; both these 
facts support the view that in Haematopinus, as in so many other cases, 
the follicle epithelium cooperates in the formation of the yolk. The 
