3i6 SUMMABY OF CURRENT RESEARCHES RELATING TO 



In the frog they are the osseous medulla and the spleen, but in this 

 animal the differences between the blood of these and other parts is 

 not so well marked as in the pigeon. The osseous medulla appears 

 to be the most important factor in the modification of the develop- 

 ment of the colourless blood-elements, but it must be remembered 

 that, without this medulla, there are developed colourless cells, which, 

 taking up haemoglobin, become converted into red blood-corpuscles. 

 In some of the cases where the medulla is wanting or reduced we find 

 that the spleen is of considerable size (eels) ; at the same time, this 

 organ may be extirjiated and fresh cells be still produced. 



No unimportant part appears to be played by the lymph-sinuses, 

 and attention must be given to such causes as are due to the slowing 

 of the blood in some of the organs in which white corpuscles seem to 

 be most largely developed. 



Origin and Destiny of Fat-cells.* — Some light is thrown upon 

 the problem of the origin and destiny of fat-cells by the observations 

 of Mr. S. H. Gage upon those of Necturiis. 



In the subcutaneous connective tissue of this creature the 

 Microscope revealed the presence of fat-cells in all stages of growth : 

 large branched cells with one or more fat-drops ; cells containing one 

 or two small fat-drops and a large one ; and some large unbranched 

 cells entirely gorged with fat. The pigment-cells were sometimes 

 partly gorged with fat, and some small round or oval cells also con- 

 tained fat. 



Thus it would appear that, as maintained by Virchow, Frey, Klein, 

 and others, fixed or branched connective tissue corpuscles may become 

 modified into fat-cells, and also, as asserted by Czajewicz, Rollett, and 

 others, migratory corpuscles may become quiescent and turn into 

 reservoirs of fat. After a Nedurus has been kept upon sparse diet 

 for some time, the adipose tissue shows but few gorged cells, many 

 transitional forms, and a greater proportion of branched cells without 

 fat, thus proving that the fat-cell is simply a store of food, and that, 

 when their store is used, the cells revert to their primitive condition 

 of branched or unbranched cells. 



Embryology of the Milk-glands, f — G. Eein summarizes the 

 results of his extended researches on the development of the milk- 

 glands. The same type of formation was found in all the species 

 investigated. Gegenbaur has maintained that the majority of mammals 

 have their teats formed by an upgrowth of the area in which the lactic 

 glands are developed ; but that in ruminants there is another type, 

 the glandular area forming a depression, the walls of which grow up 

 around it into a teat. Eein, however, demonstrates that the ruminants 

 conform to the usual development. His investigations may be sum- 

 marized as follows : — 



The first trace of the milk-gland appears very early, usually when 

 the visceral clefts are closed ; in man, during the second month. The 

 gland first appears as an ingrowth of the epidermis. The connective 



* Amer. Natural., xvii. (1883) p. 444. 



t Arch. f. Mikr. Anat., xxi. (1882) p. 678. Cf. Scicuce, i. (1883) p. 53. 



