180 



BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



7. Absorption by Mesenchyme. Only of late years have we come 

 fully to appreciate the great r61e played in ontogeny by the devour- 

 ing capacity of mesenchyme. It is now 

 fully established that such migratory pro- 

 toplasmic bodies — phagocytes — are the 

 most important agent in the degenerative 

 processes which larvae undergo in their 

 metamorphoses. 



This is well shown in Insects (Figure 

 10), in Bryozoa probably, in Ascidians, and in the frog. 



The secreting activity of mesenchyme has already been classed under 

 general processes. No doubt mesenchymatous cells perform various 



Fig. 9. 



Fig. 10. 



other functions in the body besides transportation, digestion, and secre- 

 tion, but these either have little effect on the form or concern only 

 histogenesis. 



II. Ontogenetic Processes occurring in Elongated Protoplasmic 

 Bodies — Fibres, Threads, Cords, Tubules. 



Falling under this head we may recognize, first, certain general 

 changes due to growth, such as increase in length or in thickness. 

 These may affect either the whole body or its parts, and may lead 

 to a diminution or increase in size. 



Fig. 9. Section through the transported bud of Dolchinia, showing the amoeboid 

 transporting cell. (See K. & H., Fig. 839.) 



Fig. 10. Sections through the abdominal imaginal disks of the hypodermis of 

 Musca A, from the larva. B, from the young pupa. In B the phagocytes (p.) 

 are in the act of devouring the larval hypodermis (/(.), which is replaced by the 

 superficial growtli of the imaginal disk (d.). K. & H., Fig. 530. 



