Royal Microscojpical Society. 63 



force which was transmitted from the hexagonal cells of the um- 

 bilical vesicle to the large mother-blood corpuscles is now becoming 

 extinct, and suffices only for the generation of one or two embryo- 

 corpuscles, A portion of the increase of the new coloured blood 

 corpuscles must therefore already be derived from the permanent 

 blood-formative organs. In the embryo of twelve weeks, the spleen 

 is found still more considerably developed. Its form is not any 

 more oblong as before, but more contracted ; it is now also further 

 removed from the stomach, and ready to take its future permanent 

 position. The numerous elements of the blood (Fig. 6), already 

 described, which it contains, show sufficiently that it is now per- 

 forming its function to its full extent. As far as the development 

 of the lymphatic system is concerned, it probably stands in a certain 

 relationship to that of the spleen and the blood-vessels in general. 

 While, namely, a number of lymphatic glands are still in their first 

 stages of development, others must have sufficiently advanced to 

 assume the performance of their function. 



In the preceding pages I have spoken of the spleen and the 

 lymphatic glands as of the permanent blood-formative organs, and, 

 in so doing, only endorsed the now prevailing opinion of other 

 observers regarding their function. But this essay would not 

 seem to be complete if I failed to subject to a somewhat closer 

 consideration the formative process taking place within the organs, 

 especially within the spleen. In addition to this, the views regarding 

 the exact mode of the metamorphosis of the colourless into the 

 coloured blood corpuscles, which, as it seems, still differ from one 

 another, determine me also to add a few remarks upon the subject. 

 The question to be answered is : Does the entire colourless blood 

 corpuscle, or only the nucleus within it, take part in this meta- 

 morphosis ? 



To arrive at a satisfactory sohition of this question, it is first 

 necessary to take into a closer consideration the origin and develop- 

 ment of these bodies. In regard to their origin there remains, 

 according to the most recent researches of several observers con- 

 cerning the structure of the spleen and lymphatic glands, but little 

 doubt that it has to be sought in the tissue, that is, in the fibrous 

 meshes of these organs. These meshes, extending throughout the 

 pulp of the spleen, lodge, as is known, a considerable number of 

 free nuclei and cells of different sizes. The former represent the 

 greater part of these elements, and, judging by the obvious differ- 

 ence of their diameters, are found in different stages of development. 

 They are bounded by a fine double contour, and contain a number 

 of fine granules. The cells are also distinguished by a fine double 

 contour, and contain from one to three nuclei. Besides these 

 elements, a multitude of countless granules, as also a number of 

 colourless and coloured blood corpuscles are observed. The latter, 



