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MCMURRICH. 



EXPLANATION OF PLATE VIIL 



Fig. 54. Blastoderm of Porcellio at stage when the mes-endoderm cells are 

 beginning to sink beneath the surface. 



Fig. 55. Section through a blastoderm of Porcellio of the same age as that 

 of the preceding figure, showing the lower layer cells in the blastoporic region. 



Fig. 56. Blastoderm of Porcellio at stage just before the scattering of the 

 mes-endoderm cells. 



Fig. 57. Blastoderm of Armadillidium at the time of differentiation of the 

 ectodermal teloblasts. 



Fig. 58. Blastoderm of Armadillidium with the ectodermal teloblasts more 

 perfectly differentiated. 



Fig. 59. Embryo of Armadillidium, commencement of teloblastic growth. 



Fig. 60. Section through ovum of Ligia at the time when all the cells have 

 reached the surface. 



Fig. 61. Blastoderm of Ligia at stage when the mes-endoderm cells are sink- 

 ing beneath the surface. 



Fig. 62. Posterior portion of embryo oi Ligia showing the mesoblasts. Ill- 

 F7/ = thoracic segments ; 1-6 = abdominal segments ; t = telson. 



Fig. 63. Posterior portion of embryo of Cymothoa showing the mode of 

 division of the mesoblasts. 



Fig. 64. Posterior portion of embryo of Cymothoa showing the ectodermal 

 and mesodermal teloblasts. 



