178 



BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



Lamellibranchs, the muscles of the foot of Gastropods (K. &, H., Fig. 

 556, s. m.), and the lymph glands and spleen ot Vertebrates (M., p. 414). 



The reverse process to the aggregation of mesenchymatous cells is 

 their Dispersal, and this has probably been brought about by the 

 opposite cause to that producing aggregation. Since, however, this is 

 a process taking place in a protoplasmic mass, its consideration must 

 be deferred. (See page 194.) 



"We have been considering the different forms into which mesenchy- 

 matous elements aggregate themselves in the formation of one body ; it 

 now remains to consider the processes taking place between mesenchyme 

 and other protoplasmic bodies. Of these processes I recognize at present 

 four, viz. : the attachment of mesenchymatous cells to a body, following 

 their migration thither; the encapsuling and interpenetration by a mass 

 of mesenchyme ; transportation by mesenchyme ; and absorption by 

 mesenchyme. 



_^J/a.a fam»re«. 



Fig. 6. 



Fig. 7. 



4. Attachment of Mesenchyme to another body. This process occurs 

 in the union of the muscles of Lamellibranchiata, Annelida, Crustacea, 

 and Bryozoa (Figure 6) to the hard parts of these animals, and of ten- 

 don to bone, in Vertebrates. 



5. Investment and Interpenetration, by Mesenchyme, of a mass — either 

 some other organ of the body or a foreign substance, like a parasite — is 

 a not uncommon process. Especially marked is this process in the 

 Tunicata (Figure 7), where migrating follicle cells encapsule and finally 



Fig. 6. Sections through the body wall of the Bryozoan, Paludicella ; (a) young, 

 (b) adult; illustrating the process of attachment of mesenchymatous muscles to the 

 cuticula. • 



Fig. 7. Section of the germ disk of Pyrosoma, showing migrating follicular cells 

 surrounding the blastomeres. (See K. & H., Fig. 771.) 



