130 Miscellaneous. 



the formation of the whole of the limbs that the outer layer is 

 divided oif in the shape of more columnar cells. Subsequently, in 

 the stage which is ready to emerge from the e^^, we observe the 

 appearance of the refractile nuclei and the pigment-mass in this 

 ectodermal rudiment. 



It is interesting to note that at this stage I have observed a 

 formation of the ectodermal invagination in the base of the second 

 antenna. This invagination approaches the closed mesoderm sacs. 

 It is probable that this structure becomes the antennary gland. 



At this period I also observed the formation of a pair of ecto- 

 dermal invaginations into the branchial chamber, which gradually 

 become modified into sacs. 



As regards the mesoderm cells, these form no regular somites, 

 but are quite irregularly distributed. Besides the muscles, the heart 

 and the generative organs are also formed from these cells. 



Until the appearance of the pigment in the eye, the heart arises 

 at the boundary between the thorax and abdomen. Here there 

 appears the earliest rudiment of the heart upon the dorsal side in 

 the form of a paired aggregation of the mesoderm cells. Cells are 

 protruded from the ventral side of these masses, and form the ventral 

 wall of the groove. The dorsal side of the heart remains for a 

 certain time open and covered by the ectoderm. The mesoderm 

 cells of the back soon appear from these same lateral masses, and 

 thus the oval sac of the heart is constituted. 



The sexual organs arise in the latest stages of embryonic life, and 

 are situated as a paired mesodermal rudiment in the region of the 

 mid-gut beneath the heart. Here certain mesoderm cells rapidly 

 increase in bulk, and give rise to the commencement of the genital 

 cells. 



The formation of the stomodseum takes place earlier than that of 

 tlie proctodaeum. Eoth arise as invaginations of the ectoderm. 

 The mid-gut is produced from the cell-material of the endoderm, 

 and its development proceeds from two primitively separate endo- 

 dermal rudiments. The posterior rudiment has the form of two 

 shells (cups), and lies in intimate relation to the invagination of the 

 hind gut. The lips of the posterior shell are directed forwards. 

 Simultaneously a similar aggregation of endoderm cells is also formed 

 in the region of the stomodaeum. The lips of the anterior shell, on 

 the contrary, are directed backwards. At this time the inner lips 

 of the anterior and posterior shell fuse together, and thus there are 

 formed two rudiments, which are composed of columnar cylindrical 

 cells. Their edges grow towar.ls each other, although at the 

 moment of the escape of the embryo from the egg they have not 

 yet united, so that a portion of the dorsal and ventral walls of the 

 mid-gut stiU consists of scattered cells. At this time there may 

 already be observed in the posterior endodermal sac a division in a 

 longitudinal direction, which leads to the formation of the first 

 hepatic sacs. 



