DEVELOPMENT OF THE SPLEEN. 361 



cells ; but whether this proceeds from the outgrowth of a few 

 cells, as Peremeschko maintains, or from the detachment of the 

 peripheric protoplasm of numerous cells,! am not able to decide. 

 The further development of the organ occurs tolerably rapidly, 

 so that in the human foetus of eight centimeters in length 

 the various constituents are already differentiated. The cells 

 lying beneath the peritoneal epithelium become elongated, and 

 form fusiform nucleated bodies, and similar ones at an early 

 period invest the larger vessels. From both small processes are 

 given off, which grow towards one another, and represent the 

 commencement of the trabecular system. Along the arterial 

 branches, denser accumulations of small nucleated cells may 

 already be discerned, which are conspicuous in tinted prepara- 

 tions by their deep colour, and these form by far the chief consti- 

 tuent of the pulp. This consists of cells with from one to three 

 nuclei and a delicate intercellular substance, forming plexuses, 

 the interstices of which are constantly filled with blood corpuscles. 

 According to Peremeschko, there are now developed larger pro- 

 toplasmic corpuscles in the tissue of the pulp containing from 

 two to six nuclei, that are capable of performing amoeboid move- 

 ments, and which, towards the end of embryonic life, atrophy. 

 In the further course of development the several constituents 

 increase in volume, and a part of the fusiform cells of the 

 capsule and the vascular sheaths develop into smooth muscular 

 tissue. The arterial sheaths, containing numerous cells, are 

 clearly distinguishable from the pulp, and from the middle of 

 embryonic life the Malpighian corpuscles are recognisable. The 

 cavities of the pulp may, about this time, be artificially injected 

 (Peremeschko). From the commencement of differentiation of 

 the several constituents of the organs, as this author has 

 pointed out, the cells of the pulp appear paler and more 

 delicate than those of the arterial sheaths. To explain this 

 it must be borne in mind that both of these morpholo- 

 gical elements develop from different textural formations, 

 the pulp developing from the walls of the rootlets of the veins, 

 the arterial sheaths with their Malpighian bodies from the 

 connective tissue investing the arteries. It is of importance 

 to establish this difference, because it furnishes the key to a 

 series of comparative anatomical and pathological observa- 



