208 SUMMARY OF CURRENT RESEARCHES RELATING TO 



sinus, but it becomes more and more rich in blood-vessels and nerve - 

 ramifications. 



The thymus is essentially a dual structure ; there is a connective 

 reticulum intermingled with an epithelial syncytium. To the second 

 belong the secreting cells, Hassall's bodies^ the plasmodes, cysts, and 

 ciliated or mucus elements. To the former belong the lymphocytes,, 

 the phagocytes with multiple inclusions, the histogenic granulocytes, 

 the globular pseudomyoid elements. In the lancelet the parapharyngeal 

 groove is secretory, perhaps digestive. In the young Ammocoete the 

 external secretion persists ; in the old Ammocoete the secretion diminishes 

 and the organ becomes lymphoid. In fishes the lymphoid function 

 prevails, but there is also internal secretion. In adult amphibians the 

 proper thymic function becomes twofold ; the lymphocytes are leuco- 

 poietic ; the epithelial function plays a role only during inanition, when 

 the secretion has a cytolytic influence. 



The parapharyngeal grooves persist through life in Amphioxus ; in 

 the adult lamprey the organ loses its lymphoid population and becomes 

 sclerous and fatty ; the same regression is seen in attenuated form in 

 fishes ; in higher vertebrates the thymus disappears in adult life. 



Structure and Function of Thymus.* — A. P. Duslin re-states his 

 conclusion that only the small thymic cells represent the fundamental 

 and specific part of the thymus. The epithelioid, myoid, ciliated, and 

 other elements are inconstant and metaplastic. The small thymic cells 

 are essentially proliferating elements, which form a nuclein-reserve dis- 

 tributed according to the needs of the organism. The thymus is one 

 of the centres for the regulation of nuclein-metabolism. 



Culture of Isolated Retina.f — Ch. Champy gives a detailed account 

 of the behaviour of the various layers of the isolated retina of rabbit 

 and tortoise. The degeneration of nervous and sensory elements varies 

 in mode and rate. There is rapid pycnosis of the rods, the bipolar cells, 

 the horizontal and amacrine cells. It is usually slower for the cones 

 and ganglion cells. The last have most power of persistence, partly 

 perhaps because of their abundant chromatic cytoplasm. The elements- 

 of the neuroglia survive and multiply, when the adjacent elements are 

 dead. There is de-differentiation. Indifferent cells are formed which 

 absorb the differentiated parts. There is evidence, therefore, that 

 differentiated elements may become phagocytic. 



Culture of Excised Thyroid. | — C. Champy finds that the excised 

 thyroid retains for a short time in vitro part of the normal activity of 

 its tissues. There is a gradual cessation of a function, mainly automatic. 

 Then de-diiferentiation begins. The thyroid cell shows direct division,, 

 and it absorbs its enclosed bodies. The proportion of vegetative to 



* Arch. Zool. Exp6r., Iv. (1916) Notes et Revue, No. 5, pp. 95-109. 



t Arch. Zool. Exp6r., Iv. (1914) pp. 1-18 (23 figs.). 



J Arch. Zool. Exp6r., Iv. (1915) pp. 61-79 (1 pi. and 11 figs.). 



