Royal Society. 381 



sent, and from the development of those structures occurring in a 

 similar manner in each. 



These glands are developed between the 6th and 7th days as two 

 separate masses of blastema, one at each side of the root of the neck, 

 close to the separation of the carotid and subclavian vessels, and be- 

 tween the trachea and the branchial clefts, but quite independent, as 

 far as regards their development, of either of those parts. Their 

 minute structure at an early period closely corresponds with that of 

 the spleen and supra-renal glands. Later, when the gland tissue of 

 which the thyroid gland ultimately consists is formed, it is developed 

 in a manner precisely similar to the same tissues of the spleen and 

 supra-renal glands, a fact which shows the analogy they bear to one 

 another. 



From these observations the author concludes that a close analogy 

 exists between the glands already described, so that the propriety of 

 their classification under one group, as the " Ductless Glands," may 

 be considered clearly proved. And although the spleen by many 

 has been excluded from them, the author considers that its classifica- 

 tion with them is correct, for the following reasons : — 1st. From its 

 evolution being similar with that of the supra-renal and thyroid 

 gland ; '2nd. from its structure, which at an early period closely 

 corresponds with them ; and 3rdly, from the development of its 

 tissues following the same law as that upon which the tissues of the 

 allied glands are formed. 



Jan. 29. — The reading of Dr. Handheld Jones' paper, " On the 

 Structure of the Liver," was resumed and concluded. 



Dr. Leidy and Professor Retzius, with Muller, Weber and 

 Khronenberg, maintain the existence of plexuses of ducts in the 

 parenchyma of the liver containing the cells in their tubes. Some 

 other anatomists, especially Gerlach, believe the ducts to be pro- 

 longed into the lobules of the parenchyma, under the form of mere 

 intercellular passages without walls. 



Injections of acetate of lead in saturated solution, thrown into the 

 ductus communis choledochus, produce appearances which seem to 

 confirm the latter view. The author, however, believes them to be 

 fallacious, and that the ducts really terminate, as he has described them 

 in his former paper, by closed extremities, either rounded and even, or 

 somewhat irregular. Further details are given of the condition of 

 the ultimate and penultimate ducts in the several vertebrate classes. 



In the class of Fishes, the minute ducts most commonly appear as 

 solid cylinders of soft granulous substance, in which scarce anything 

 but some oily molecules are to be discerned ; but not very unfre- 

 quently two other conditions are observed, which seem to illustrate 

 very well the active character of the function of the duct. In the 

 first the granulous matter exists in much smaller quantity, and the 

 nuclei imbedded in it are consequently seen much more distinctly; 

 their presence is thus unequivocally determined ; it is shown that 

 there is no real difference between the duets of the fish's and those 

 of the mammalian liver, only that the granulous matter is usually 

 accumulated in the former more abundantly than in the latter. The 



