REPORT OF THE DIRECTOR I918 26I 



brane closely surrounding the embryo and separating it from the 

 more fluid envelop. 



The eggs were very slightly pigmented on one side when found 

 but it is highly probable that when deposited they were less so. The 

 unpigmented parts were given a light tinge of color by the yolk. 

 Deposited as they were in damp moss, it was often necessary to 

 wash the eggs or remove the outer envelop entirely to free them 

 from adhering bits of rubbish. 



Development oj the Embryo 



When found (May 14th) the eggs were well advanced in develop- 

 ment, the earliest stage noticed having the medullary folds fully 

 formed though not yet approximated. As early segmentation and 

 gastrulation stages are normally passed through rapidly, the eggs 

 probably had not been deposited longer than 48 to 72 hours before 

 being discovered (plate 6, figure i). There is no trace of the blasto- 

 pore although such early disappearance may be considered unusual. 

 Of the series of eggs examined, only one revealed the conditions 

 noted above, the remaining specimens being considerably more 

 advanced. Another specimen taken the same date has the embryo 

 well defined (plate 6, figure 2), with a median longitudinal depressed 

 line marking the union of the medullary folds. Body divisions are 

 not apparent in this stage unless the slight widening of the anterior 

 end of the embryo be considered as defining the limits of the head. 

 About two-thirds of the circimiference of the egg is occupied by the 

 encircled embryo in this stage. 



May i6th. Definite head and body regions are evident. Back 

 of the head a slight swelling indicates the position of developing 

 tissue for gill and arm buds. In front, the head is slightly free. 

 The egg is considerably elongated but whether from distortion or 

 influence of the embryo is not apparent (plate 6, figure 3). 



May 19th. The development of tissue, which barely indicated 

 the position of gill and arm buds in the preceding stage, shows 

 marked increase and with the head comprises fully one-half the mass 

 of the egg. The embryo is folded upon itself, the head, gill and 

 arm regions occupying one hemisphere, the yoke mass the other. A 

 slight narrowing of the head in front and more definite pigmentation 

 give indications of forming eyes and snout (plate 6, figure 4). 



May 2 1 St. The eye regions are highly pigmented and the tissues 

 of the developing gill and arm buds greatly increased in thickness. 

 The three primary divisions of the body, head, trunk and tail are 

 now recognizable; the tip of the tail is in contact with the under 



