The Hog Louse 709 



as a true yolk chamber. This chamber remains small, there is no boundary 

 between it and 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 into scattered fragments until finally only epithehal 

 nuclei remain and these have migrated into the interior 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, ball-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 LXVI, 10). Gross has never seen cell division following 

 the amitotic division of the nuclei, and in the hght 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 cells 

 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 



