472 RICHAED EVANS. 



Pig. 27. — X 1000. Section of the lower surface of an individual which 

 contains a few loose cells in addition to the plasmodial aggregations, and is 

 derived from type D. The small group of loose cells {g-c.) should be 

 specially compared with the similar groups in Fig. 7 a. 



Pig. 28. — x 1000. Portion of a section of an individual slightly more 

 advanced than those represented in Pigs. 24- b and 31. It shows two chambers 

 which are exceedingly different in the character of their individual cells. In 

 the upper one all the cells and their nuclei are like one another, while in the 

 lower one they are not so. The nuclei of the cells (c. c, g. c.) of the upper 

 chamber resemble those of the chamber cells of Pigs. 24 b and 31, while those 

 of the cells {c.c.,fl.c.) of the lower chamber are far more like the nuclei 

 of the chamber cells seen in Pigs. 19, 20, and 21. The cells c. c, g. c, have 

 evidently been derived from cell groups, while the cells c. c.,fl. c, have 

 been produced from flagellated cells, and have not as yet attained their 

 definitive structure, after passing through a series of changes in connection 

 with the formation of the plasmodial aggregations. 



PLATE 40. 



Pig. 29. — x 350. Complete section of a pupa from a larva of type C. The 

 flagellated layer has completely disappeared from the lower surface, while it 

 is still complete on the upper surface. The flagellated cells which have 

 travelled in from the lower surface are already in process of forming plasmodial 

 aggregations. The flat epithelium of the lower surface is almost complete, but 

 the cells witli granular nuclei still remain inside the flagellated layer on the 

 upper surface. Plagellated chambers (C.) are fully formed. The larval cavity 

 is still retained, and will probably become a part of the exhalant system and 

 gastral cavity. 



Pig. 29 a. — X 1000. A portion of the upper surface of the same larva as 

 Pig. 29. It shows the flagellated layer absolutely complete at the same time 

 as fully formed flagellated chambers. The yolk bodies are rather numerous, 

 and their remains are seen even in the collar-cells. It is quite possible that 

 these small bodies seen in the collar-cells here are the same as the refringent 

 bodies seen in preparations mounted in glycerine, after maceration with osmic 

 and staining with picro-carmine (cf. Pigs. 38 and 39). 



The flagellated chamber marked C. is being constricted to form two chambers. 

 The two chambers situated further in have been produced in the same way, 

 the space between them becoming an exhalant canal. 



Pig. 29 b. — x 1000. A portion from the lower surface of a section from 

 the same larva as that drawn in Pig. 29. The flagellated epithelium has com- 

 pletely disappeared, and the flat epithelium is well formed. The plasmodial 



