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, amd this has probably been brought about by the 
opposite cause to that producing aggregation. Since, however, this is 
a process taking place in a protoplasmio 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 protoplasmie bodies. Of these processes I recognize at present 
four, viz.: the attachment of mesenchymatous cells to à body, following 
their migration thither ; the encapsuling and interpenetration by a mass 
of mesenchyme; transportation by mesenchyme; and absorption by 
mesenchyme. 
Follicle 
Cells, i `> 
dies 
Fia. 6. Eta. 1, 
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 
sells encapsule and finally 
Tunicata (Figure 7), where migrating follicle « 
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 
cutícula. 
Fig. 7. Section of the germ disk of Pyrosoma, showing migrating follicular cells 
surrounding the blastomeres. (See K. € IL, Fig. riga 
