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BERTRAM G. SMITH 



homogeneous material, much less dense than either of the pre- 

 ceding. This outer layer is produced to form the stalk by which 

 the capsule is attached to some solid object. As seen in optical 

 section, the lamellae of the two inner layers have a somewhat 

 sinuous or wavy outline. Leaving the stalk out of account, the 

 entire structure bears a close resemblance to the gelatinous envel- 

 opes of the frog's egg. In the early stages of development of the 

 embryo, the dense inner layer of the capsule fits so closely that it 

 is not clearly differentiated from the embryo; this layer is best 



Fig. 4 Optical section through an egg capsule, and surface view of an embryo, 

 of Necturus. The embryo is shown in a stage with neural folds, when the capsule 

 is slightly separated from it by a space filled with water. X 4. 



studied after the embryo has passed the gastrula stage, when a 

 narrow space, filled with liquid, appears between the embryo and 

 its capsule (see fig. 4). This space is not strictly homologous with 

 the similar space that appears much earlier in the egg of Cryp- 

 tobranchus; for in Cryptobranchus the space appears between 

 the gelatinous envelope and the vitelline membrane (zona pellu- 

 cida of the ovarian egg) which remains in close contact with the 

 egg, while in Necturus the vitelline membrane apparently func- 



