MUSEUM OF COMPARATIVE ZOOLOGY. 99 



Fig. 3. The same view of another egg. 

 " 4. End view of an egg at the stage of the primitive cumulus. 

 " 6. View upon the anterior end of the egg from which Fig. 2 was drawn. 



The larger polygons are boundaries of yolk masses, the smaller those 



of blastoderm cells. 



PLATE II. 



Fig. 6-11 are side views of eggs, and are arranged in the order of their sequence 

 in development. 



■" 6. Left side of the embryo :it the stage which exhibits six protozonites. 



" 7. View of the right side at the stage marked by the beginning of the 

 appendages. 



" 8. A more advanced embryo (left side) with incurved permanent appendages 

 and four pairs of provisional appendages. 



" 9. A somewhat oblique view of the right side during the period of reversion, 

 showing the rudimentary terga (trg.), also an increase in the distance 

 between the cephalic and caudal lobes. 



" lO. Embryo (left side) wlien reversion is nearly completed, showing the per- 

 sistence of the two posterior pairs of provisional appendages, and 

 also their change in position to the posterior part of the body. 



" 11. Embryo after the reversion is completed ; tlie last two pairs of provisional 

 appendages are being modified to form the spinning mammillae. 



PLATE III. 



Fig. 12. The head and tail lobes at the stage when the appendages begin to 

 appear. 



" 13-17 form a series of dorsal views during reversion. 



" 13. Dorsal view of an embryo at the beginning of reversion. 



" 14. An embryo a little further advanced, to show the separation of the head- 

 and the tail-lobes, and also the increase in the dorsal extension of the 

 tergites. 



" 15. A similar view of an embryo a few hours older than the preceding. 



" 16. Dorsal aspect of a still older embryo, in whicli the tail-lobe is just disap- 

 pearing from tlie dorsal surface. 



" 17. An embryo at about the stage represented in Fig. 11. 



PLATE IV. 



Fig. 18-23 present a series of ventral aspects. 

 " 18. An embryo at the stage which shows six protozonites. 

 " 19. An embryo showing the beginning of the appendages ; it is of the same 



age as that shown in Fig. 7. 

 " 20. View of the caudal lobe at about tlie same stage as is represented in 



Fig. 8. 

 " 21. Ventral view during tlie period of reversion. The embryo corresponds 



nearly with the stage represented in Figs. 10 and 16. 

 " 22 Ventral aspect of the embryo from which Fig. 14 was drawn. 



