LYMPHATICS OR ABSORBENTS. 993 



sembling the shape of the blood corpuscles of the Amphibia ; the nucleus soon 

 divides into two, or even into three or four portions, or young nuclei ; the walls 

 of the so altered cells then become constricted between these young nuclei, and, 

 ultimately, the cells divide into as many new cells as there were nuclei ; this 

 process, it is supposed, may be repeated over and over again. 



After a time, corresponding with the date at which the liver begins to grow, 

 this process of subdivision of the primitive nucleated red corpuscles ceases, and 

 then multitudes of colorless nucleated cells appear, especially in the blood of 

 the liver and of the spleen, and also in the lymphatic system ; and either with- 

 out, or with, previous multiplication by subdivision of their nuclei, constric- 

 tion of the cell-wall, and actual partition, they acquire, even within the spleen 

 and liver, some red coloring matter, and are changed into nucleated red corpus- 

 cles. 



Both sets of these spherical, nucleated red corpuscles, are ultimately con- 

 verted, by a slight diminution of size, by a flattening of two opposite "sides, 

 and by the gradual wasting and final disappearance of the nucleus, into the 

 typical non-nucleated disc-like red corpuscles of the fully formed blood. This 

 condition exists at, or a considerable time before, birth. After birth, during 

 the growth of the body, and in the adult, the red corpuscles of the blood 

 are developed from the colorless ones, as already elsewhere described (p. 729). 



The white blood-corpuscles are evidently the unaltered, colorless, nucleated 

 cells, derived, at first, from the blood itself, afterwards from the liver, and per- 

 manently from the spleen and the lymphatic system. Under certain circum- 

 stances, as in inflammation, colorless blood-corpuscles may perhaps originate 

 in the blood itself, within the general capillary system. 



The plasma of the blood, at first the product of the liquefaction of the inter- 

 mediate blastema or matrix, probably effected under the agency of the forma- 

 tive cells, is afterwards the complex result of various acts not only of a for- 

 mative, but also of an absorptive and excretory kind. 



Lymphatics or Absorbents. 



The mode of formation of the principal absorbent trunk, the thoracic duct, 

 is probably like that of the primitive bloodvessels. 



The small lymphatics, according to observations made in the tadpole's tail, 

 originate by the junction of nucleated cells, in the same way as the large cap- 

 illaries ; but they are said to anastomose much less frequently. The extension 

 of the absorbents into newly growing tissues is effected, as in the case of the 

 capillary network, by the formation in the new tissue of peculiar cells, which 

 branch out, and join certain very fine processes, given off from the lymphatics 

 already developed. These stellate cells are said to be more jagged in their out- 

 line than those of the capillaries. 



The lymphatic glands are believed to be developed from clusters of lymphatic 

 vessels, which give out projections, afterwards converted into the alveoli or 

 cells of the cortical portion of those glands. 



The chief microscopic structural elements of the lymph and chyle, the small 

 and large nucleated corpuscles, most probably originate in the lymphatic ves- 

 sels and glands, by subdivision of pre-existing corpuscles, and perhaps multi- 

 ply by subdivision. Probably also some of those seen in the chyle and intesti- 

 nal lymph, before it reaches the mesenteric glands, originate in the solitary or 

 agminated glands. They also seem to be formed in the spleen, thyroid, and 

 thymus glands, or even in the interior of the commencing lymphatics. At 

 first, these cells are minute, and their envelope closely surrounds the nucleus. 

 In this form, they constitute the small lyrnph corpuscles. They grow into the 

 larger ones, by the deposition of soft granular matter between the exterior and 

 the nucleus. They also multiply by elongation, subdivision of the nucleus, 

 constriction of the delicate cell-substance, and partition into two new cells, 

 each having its own nucleus. 



The molecular base of the chyle is apparently the result of a process of ag- 

 gregation of the simplest kind, whilst the fluid part of the lymph and chyle 

 may be regarded as an extremely diffluent blastema or fluid matrix. . 



63 



