Royal Microsco^eal Society. 57 



corpuscles, and pursue their formation further through the different 

 stages of embryonic hfe. 



It will be remembered, that among those blood corjjuscles 

 issuing from the orifices of the canals, there were some which con- 

 tained besides those concave depressions — " traces of a preceding 

 generation" — still a younger brood of three to four embryo-cor- 

 puscles within their substance (Fig. 2), This fact indicates that 

 the process of multiplication of these bodies in this early period of 

 embryonic life must take place quite rapidly. Another fact, worthy 

 of notice, was the entire absence of colourless blood corj)uscles, but 

 which is fully explained by the absence of those organs, viz. spleen 

 and lymphatic glands, which, at a later period, are concerned in 

 their formation. In fact, those colourless bodies only appear simul- 

 taneously with the development of the latter-named organs, and at 

 a time when the primary endogenous process of multiplication has 

 become much slower in its course, eventually ceasing almost 

 entirely. 



With some embryos of 16 to 20 mm. in length, which I ex- 

 amined, I had no opportunity to examine the blood in its fresh 

 condition, either because the examinations of the nervous tissues 

 first claimed my attention, or that, for want of time, I was com- 

 pelled to put the specimen, for the sake of preservation, in a weak 

 solution of chromic acid. At a subsequent examination of the pia 

 mater of the spinal marrow, however, I found that the blood left 

 behind in the vessels contained no more of those large mother-blood 

 corpuscles, enclosing three or more embryo-corpuscles. Although 

 I still met with a number of bodies, showing two to three concave 

 depressions, no more than one embryo-corpuscle was observed 

 within, their substance. Their diameter, also, had considerably 

 diminished. The greater portion of the blood consisted here already 

 of fully-developed corpuscles. 



In embryos of eight to nine weeks I first had the opportunity of 

 making a close examination of the coloured blood corpuscles in their 

 fresh condition. Judging from the advanced development of the 

 heart, and especially of the smaller blood-vessels, the circulation of 

 the blood at this period must ah-eady take place quite regularly. 

 By far the greater majority of the blood corpuscles are fully 

 developed. The large mother-corpuscles, containing several em- 

 bryos, have disappeared, but a considerable number of those smaller 

 ones, enclosing only one embryo-corpuscle, are still there. The 

 process of multiplication accordingly occurs now much more slowly. 

 A weak solution of chromic acid discolours the mother- bodies and 



nuclei; its interior surface was lined by a tesselated epithelium, the hexagonal 

 cells of which contained very clear oval nuclei. Upon this rested very loosely 

 a delicate spider-web-like layer of fibrous tissue. No trace of the formation of 

 embryonic blood-vessels was to be seen. The ovum was at its expulsion still 

 surrounded by the entire membrana decidua. 



