384 Development of tlie Lympliatic ^NTodes in the Pig 



showing seven microscopic nodes. These different small glands repre- 

 sent all stages in development. 



In the figure there is an ahundant plexus of lymphatic ducts and 

 around this plexus is a group of small follicles. Two of these nodes, 

 marked a, consist of a collection of lymphocytes around a tuft of blood 

 capillaries. Studied through serial sections, these small follicles (a) 

 have no lymphatics whatever. Two of the small nodes, marked h. have 

 a single peripheral sinus around the follicle while others, marked r, have 

 an abundant plexus of lymph ducts not transformed into sinuses. The 

 node in the lower edge of the section is shown only in part. It is the 

 margin of a larger node and shows the peripheral zone of lymph ducts. 

 This entire mass of follicles will be subsequently fused with the large 

 inguinal node, which is one method of increasing the size of the nodes. 

 The inguinal node at birth contains fewer of the smaller follicles in the 

 border than at earlier stages. The study of these microscopic nodes 

 proves an important point, namely, that the lymphoid part of the node 

 or the lymphocytes in the reticulum occurs primarily with the arteries 

 and blood capillaries rather than with the lymphatics. This was sug- 

 gested by the angiogenesis of the primary node, but is proved by the fact 

 that small nodes are found around the capillaries before they are reached 

 by the lymphatics. That is to say, the follicle is primarily and essen- 

 tially associated with the artery. That the follicle occurs in the adult 

 without lymphatics is shown in the Malpighian corpuscles of the spleen. 

 In Fig. 17 is a small lymph node found in the lung of an adult pig. It 

 lies in the edge of a lymph capillary but is without a true sinus forming 

 an integral part of the node itself. 



To return to Fig. 16, the section shows that nodes which develop at 

 later stages after the lymphocytes occur in the glands, hurry through the 

 long preliminary process of the first nodes; that is to say, they begin 

 at once with a heaping up of lymphocytes around a blood-vessel. 



Themolympli nodes. — The study of the development of these nodes is 

 incomplete. It has not yet been extended to all the areas in which the 

 h^molymph nodes occur, but confined to the neck region and along the 

 course of the thoracic aorta. The liEemolymph node does not occur in 

 the neck of the pig until the embryo is about 23 cm long, showing that 

 it is a considerably later development than the lymphatic node. From 

 the time the embryo is 23 cm. long there are one or two small nodes to 

 be found near the node which forms in the center of the long plexus 

 (see Fig. 7). In the specimen at 23 cm. long the hffimolymph node is 

 in the simplest possible stage consisting of a single follicle with a 



