Charles R. Stockard all 
were loosely associated with the dorsal muscular tissue, consequently in 
the rapid growth of this dorsal tissue the lappet structure with the gills is 
left behind. The complex changes connected with the enormous growth of 
the dorsal neck tissue, the development of the large club-muscle, and the 
connection of the gill lappet tissue with the dorsal musculature are the 
principal causes operating to produce the translocation of the gills in 
the embryo. 
Fics. 33 to 36. Diagrams illustrating the change in position relations dur- 
ing the development of the gills. Fig. 33. The condition in young embryos 
when all of the branchial gills are out on the gill lappets. a, ear vesicle; VM, 
outline of the mandibular diverticulum; Hm, the hyomandibular; tg, tg’, first 
and second post-hyomandibular gills; «, point where rapid growth takes place 
causing the head to grow forward leaving: the gill area behind. Fig. 34. 
The first few gills are drawn in from the lateral lappets. 2, the rapid growth 
point; a, ear vesicle increased in size. Fig. 35. An embryo in which the 
gills have partially shifted. The two post-hyomandibular ones are in their 
original position and have decreased in extent. pl, p2, the beginning of the 
pouches in the branchial gills. Fig. 36. The gills shifted far back. The ear 
vesicles are partially anterior to the hyomandibular. The indefinite posterior 
border of the hyomandibular cleft is dotted. 
Fig. 35 shows the gills partially shifted back: the pouches, p, are 
forming near the communications of the gill tubes with the pharynx, 
the thyroidean gills have greatly degenerated and the auditory vesicles 
are seen to have moved forward in their relation to the mandibular 
arch. This forward change at such a period is probably due to a 
shortening or forward condensation of the embryonic brain. Fig. 36 
indicates the further change in the gill position. In Figs. 35 and 36 the 
posterior limit of the hyomandibular clefts are dotted to indicate that 
they fade out over the velum in a very indefinite manner as above referred 
