DEVELOPMENT OF SPELERPES BILINEATUS 213 



plane and the median plane of the embryo were more numerous 

 than cases of separation by 90.°^ 



In many cases the first plane of cleavage did not divide the 

 egg equally as has already been noted on page 180. The more 

 extreme cases of such inequality have been noted in the table 

 given below. In other eggs marked before the first plane had 

 extended far, it sometimes happened, when the centre of the 

 stained spot lay directly in the path of the advancing furrow, 

 that it has been deflected from its path, passing around the edge 

 of the stained spot. 



In 15 of the successful eggs, the first plane and the median 

 plane of the embryo coincided (table 2, page 214). In 8, they 

 formed an angle of 90° with each other. In 14, still other angles 

 were formed. 



Series E is notable because in all of the eggs, the median plane 

 of the embrj'o coincided with the first plane of cleavage. From 

 Series D we learn that ho necessary connection exists between 

 the plane of the egg which passes through the middle of the 

 blastopore and the median plane of the embryo. This lack of 

 agreement is further emphasized in the studies made upon the 

 movements of the blastopore (vide infra) . In some cases the me- 

 dian plane of the embryo did not coincide with the first plane of 

 cleavage, although it lay at one side parallel to it. 



Of all of the numerous workers, (viz., Newport '50, Pfliiger '83, 

 Roux '83 and '03, Born '84, '93 and '94, Rauber '86, Hertwig 

 '93, Jordan '93, Eycleshymer '95 and '04, Endres '95, Bataillion 

 '96, Schultze '99, Kopsch '00, Spemann '02, Morgan and Boring 

 '03, Brachet '04, and Jenkison '09), who have discussed the 

 relation existing between the first plane of cleavage and the medi- 

 an plane of the embryo in Amphibians, no one has described a 

 series of experiments in which there was an exact coincidence 

 between either the first or second planes of cleavage and the 

 median plane of the embryo. Eycleshymer's ('04) observations 

 on the eggs of Necturus are especially interesting because, although 

 the first plane of cleavage in the lower hemisphere could be fol- 



* The angle between the first plane of cleavage and the median plane of the em- 

 bryo was determined by inspection. , 



