WAITE: ANTENNAL GLANDS IN HOMARUS AMERICANUS. 203 



21. The adjacent walls of the two sacs break through at a single 

 point. There is consequently an abrupt transition — marked by the 

 mes-ectal line — from the mesodermal to the ectodermal part of the 

 organ, the epithelial cells of the two parts being from the beginning of 

 different types. This boundary persists in the adult. 



22. The organ probably does not secrete until after hatching. 



23. At hatching the lumen of the ectodermic sac increases greatly in 

 size. 



24. In the first larva the endsac is for the most part ventral to the 

 ectodermic sac. The duct leads from the ventral region of the ecto- 

 dermic sac to the exterior. 



25. At this stage the cells of both endsac and ectodermic sac (laby- 

 rinth) show evidence of secretory activity. The lumen of the ectodermic 

 sac alone contains a granular coagulum. 



26. The epithelial cells of the ectodermic sac in the first larva have a 

 vertically striate cuticuloid layer on the free end. Such a structure is 

 not present in any cells of the endsac. 



27. At this stage the epithelium of the duct differs from that of the 

 ectodermic sac in having neither a striated cuticuloid laver nor striated 

 cytoplasm, but there is a gradual transition from one kind of epithelium 

 to the other. 



28. The gland of the second larva differs from that of the first chiefly 

 in size, which increases proportionally to the increase in the size of 

 the larva. 



29. The development of evaginations from the ectodermic sac (laby- 

 rinth) begins in the third larva. In later larvse these evaginations in- 

 crease in number and size, and form anastomoses. Thus the complications 

 of the adult labyrinth result from evagination and anastomosis, not from 

 the coiling of a single tubule. 



30. Secretion by globules (as in the adult) begins in the third larva 

 and increases in amount in older larvae. 



31. The vesicle first appears in the third larva, as a large, open dorsal 

 evagination from the anterior portion of the ectodermic sac. In older 

 larvae it increases rapidly in volume and grows caudad. 



32. During larval life the chief growth of endsac and ectodermic sac 

 are in different directions. The result is that the two parts of the gland 

 revolve around an approximately antero-posterior axis, so that the endsac 

 comes to lie, as in the adult, dorsal to the ectodermic sac. 



