NOTES ON HISTOLOGY OF LINGÜLA ANATINA. 13 



ferent sizes being met with throughout almost the entire length 

 of the section. 



In young Liiigula (4.5-10 mm. in shell length) at the 

 posterior region of the dorsal and ventral body walls, where the 

 dendritic organs of Hancock: are to be developed, the peritoneal 

 layer, a very thin epithelium (PI. I., Fig. 14), is separated from 

 the outer epithelium of the body wall, next the shell, and in 

 the lumen thus formed many spindle bodies are found together 

 with the leucocytes and the compact bodies. In preparations of 

 the adult Lingula, especially in those fixed with sublimate, when 

 all the viscera are taken out before or after the fixation, the 

 dendritic organs come distinctly into view as three irregularly 

 pinnated ridges (PL I., Pig. 12) ; the central being the longest, 

 runs along the median plane ; the lateral ones along the lateral 

 body wall. Differing much from the structure seen in the young 

 individuals, the organ in sections shows that it is composed of a 

 many layered epithelium with vesicular nuclei and granular cyto- 

 plasm without cell-boundaries (PI. I., Fig. 13). In this epithelium 

 an enormous number of spindle bodies are found : a few of them 

 are directly imbedded in the epithelium, while the rest, in groups 

 of twenty or thirty lie in hollows. In the neighborhood of the 

 cavity cytoplasm becomes disorganized as in the case of the 

 epithelial ridge. 



To the curious phenomenon that such enigmatical bodies of 

 various sizes are produced in such a remarkable number from 

 definite regions, I paid not a little attention, and at last I came 

 to discover nearly all stages of transformation from the ordinary 

 blood corpuscles up to the spindle bodies. Unfortunately the 

 blood corpuscles were not found in the epithelial ridge, but in 

 the dendritic organ of young Lingula they were distinctly seen 



