Mosaic Development in Ascidian Eggs. 



171 



m'ch 



Right or Left Half Larvae. Fixed and Stained INIaterial. 



Figs. 37-40. Four half larvae from eggs which were spurted in the 2-cell or 4-cell stage and fixed 

 22 hours later. These larvae are still within the egg membranes though at a corresponding age normal 

 larvae are undergoing metamorphosis. 



Fig. 37. Right half larva, ventral view. The tail which is elongated is turned down toward the 

 dorsal side; the sense vesicle also lies on the dorsal side and is here seen through the embryo. The 

 muscle cells are chiefly on one side of the notochord but have grown over to the other side at the posterior 

 end. 



Fig. 38. Left half larva, dorsal view. The neural plate with sense spots is partly covered by the 

 end of the tail. The mesenchyme is found only on the left side. 



Fig. 39. Left half larva from the left side. The neural plate is folded so as to form a nearly closed 

 sense vesicle, in which are two sense spots. 



Fig. 40. Left half larva viewed from the left side. The neural plate is partially closed, but is 

 abnormal in form. In all of these larvae the neural plate lies on the concave side. 



