ON THE DEVELOPMENT OF NEBALIA. 387 



invests all the first five appendages (nauplius appendages and 

 maxillae) closely following all their curves and outgrowths. 

 The rest of the appendages are covered by an unbroken skin 

 which forms a general sac over them and the back. This 

 skin separates itself gradually from the parts it covers, and 

 is finally thrown off. In this stage the shell first appears as 

 a dorsal crease. Some embryos, which closely resemble that 

 last described, show the head flap, further lateral developments 

 of the shell, and pigment in the eyes ; but in these, as in the 

 last described stage, the front part of the yolk is still unen- 

 closed by endoderm. 



Sixth Stage. — In this stage he notes : 



(a) The shell valves covering the body of the embryo as 

 far back as the fifth thoracic appendage. 



[h) The head flap with its front end more rounded than in 

 the adult. 



(c) The body now segmented and covered with chitin, the 

 latter forming rows of teeth on the two segments before the 

 last, whilst in the adult these teeth surround all the six seg- 

 ments before the last in the form of belts. 



{d) Segmentation of several of the appendages. 



(e) All the yolk now enclosed by endoderm. Liver out- 

 growths which diverge in the shape of blind conical sacs lying 

 at the sides of the intestine and containing grey matter (de- 

 rived from the yolk) and some yolk. Also two shorter out- 

 growths directed forwards. 



Seventh and Last Stage, which differs only from the 

 adult in having three instead of four abdominal legs, in having 

 fewer segments in the antennas, and in having no vertical 

 split in the middle lamina of the gills of the thoracic legs. 



In one place he regrets that he saw so little in the embryos. 

 To us the wonder must be that he saw so much without the 

 help of all our modern appliances and contrivances. He 

 refers to the work of a previous observer, Kroyer, who found 

 twenty-four appendages in the adult. Kroyer was of the 

 opinion that Nebalia could not be a Phyllopod, as it did 

 not leave the brood pouch of the mother until practically an 



