110 E. R. HOSKINS AND M. M. HOSKINS 



In all stages carmine may be seen as granules free in the sinuses, 

 and ingested by the endothelium of the sinuses and by splenic 

 cells. The insert in figure 1 shows an endothelial cell that has 

 extended a pseudopodial process and engulfed a very large 

 granule. The figure also shows an endothelial cell filled with 

 carmine and apparently about to be liberated as a free phago- 

 cyte (macrophage?). In many places the ingested carmine 

 seems to be enclosed in vacuoles. 



There is a decided increase in the number of mitotic figures 

 seen in the spleen beginning with the 21-hour stage, indicating a 

 leucocytosis. 



e. Spiral-valve and stomach. In these organs there is an 

 occasional phagocyte in the capillaries that contains carmine. 

 There is no carmine outside the vessels. 



/. Gills. The large sinuses which are interposed between the 

 branchial arterial arches and the capillaries in the filaments are 

 lined with an endothelium which is very phagocytic. This will 

 be described in detail under 'Trypan blue.' In the earlier stages 

 the gills were not examined, but sections of later stages (50 and 

 96 hours) show the endothelial cells of the sinuses to be en- 

 gorged with carmine granules. Many of these cells have also 

 been 'budded off' and lie in the channel as free phagocytes. 

 This endothehum is doubtless one of the- sources of circulating 

 phagocytes in the dogsfish. 



Even the arterial arches are lined with phagocytic endothelium 

 especially along the side next to the sinuses. 



g. Heart. The l|-hour stage shows a few cells of the endo- 

 cardium that are phagocytic to carmine. The heart in other 

 stages was not examined. 



h. Blood. In all stages the blood contains free carmine and 

 granules ingested by phagocytes. The number of free granules 

 decreases in the later stages. 



B. Neutral red. Two series of experiments were conducted 

 with neutral red and to some extent with different results. In 

 1916 the sample of neutral red used seemed to form a true suspen- 

 sion, as it could all be separated from the water with ordinary 

 filter-paper. 



