I INTRODUCTORY 5 



2. Migration of free amoeboid bodies : e. g. the mesenchyme 

 cells in the Echinoderra gastrula, the lower layer cells of 

 Elasmobranchs, the blastomeres amongst the yolk-cells in Triclads 

 and Salps. 



3. Aggregation of isolated cells. 



a. Linear aggregates : e. g. the kidney of Lamellibranchs, 

 the yolk-gland of Turbellaria, capillary blood-vessels. 



b. Superficial aggregates : e. g. the blastoderm of Arthro- 

 pods, the formation of the imaginal gut-epithelium in some 

 Insects. 



c. Massive aggregates : e. g. the gemmule of Sponges, the 

 spleen of Vertebrates. 



4. Attachment of isolated cells to another body : e. g. the 

 union of muscles to the shell in Mollusca and Arthropoda, of 

 tendon to bone in Vertebrates, the application of skeletal cells 

 to the notochord. 



5. Investment and penetration by isolated cells : e. g. the 

 follicle cells between the blastomeres in Tunicata, the muscles 

 of the gut in various animals, the septa of the corpus luteum, 

 the formative cells of the vitreous body of the Vertebrate eye, the 

 immigration of the nephric cells in the Earthworm. 



6. Transportation of bodies by wandering cells : e. g. of the 

 buds in Doliolidae. 



7. Absorption by wandering cells : e. g. phagocytosis in 

 Insect pupae and in the tadpole's tail. 



8. We may place here the frequent alterations in the shapes 

 of cells, which do not apparently involve" growth : e. g. when 

 flat cells become columnar." 



II. THE MOVEMENTS OF CELL AGGREGATES. 



A. Linear Aggregates. 



1. Growth in length : e. g. the growth of the roots and stems 

 of plants, of the stolons and hydranths of Hydroids, the out- 

 growth of nerves, of the necks of unicellular glands, the growth 

 of the blood-vessels from the area vasculosa into the body of 

 the Chick embryo, of blood-vessels towards a parasite, the 

 growth of mesoblastic and other germ-bands in Annelids, the 

 back-growth of the Vertebrate segmental duct, and the like. 



