594 LOCY. 



EXPLANATION OF PLATE XXX. 



Figs. 88-112. Twenty-five transverse sections of an embryo very slightly older 

 than that represented in Fig. 16. The sections 88-100 lie in the region of the 

 cephalic plate. The following sections 105-112 lie in the neck and trunk regions. 



These sections are remarkable in bringing to light serial depressions along the 

 walls of the neural folds. They show that the serial cup-like differentiations 

 extend back of the cephalic plate. I have not been able to determine the number 

 of serial differentiations of this character in the embryo, but it is clear there are 

 several pairs behind the cephalic plate upon which I have noted in surface study 

 four pairs in addition to the eyes. X 45 diameters. 



[Figs. 1 1 3-1 1 5 were drawn from nature by Miss Tanetta Gilleland. Figs. 117 

 and 118 are taken from Kupffer's "Studien zur vergleichenden Entwickelungs- 

 geschichte des Kopfes der Kranioten," and Fig. 116 is after Froriep.] 



Fig. 113. View of the head-end of embryo of Ambly stoma in the open neural 

 groove stage, X about 10 diameters. Shows segmental folds in the neural folds 

 and a smooth neural plate. 



Fig. 114. View on the caudal extremity of the same embryo. 



Fig. 1 1 5. Embryo of Ratia palustris showing large obvious segmental folds 

 in the median plate and also smaller fainter folds in the neural ridges. The latter 

 correspond to the segments in the neural ridges in Amblystoma. 



Fig. 1x6. Embryo of Triton cristatus after Froriep. Showing large obvious 

 folds in the median plate with unsegmented neural ridges. These median folds 

 probably correspond to those in Ratia palustris and not to the metameric divi- 

 sions in the neural folds. 



Fig. 117. View on the head-end of Salamandra a/'ra, according to Kupffer, 

 showing segmental folds in the median plate but none in the neural ridges. Com- 

 pare with Fig. 115. 



Fig. 1x8. Caudal end of same embryo. 



Figs. 119-124 are sagittal sections of Squalus acanthias. X about 45 diameters. 



Fig. 119. Section of head of embryo about same age as those represented in 

 Figs. 37 and 48, showing the roof of the thalamencephalon raised into two eleva- 

 tions. 



Fig. 120. Somewhat older embryo showing the tubular-like growth of the 

 epiphysis. 



Fig. I2X. Still older stage showing reduction of the anterior part of roof of 

 thalamencephalon and great increase in depth of the furrow in front of the 

 thalamencephalon. 



Fig. X22. Older stage in which the paraphysis has made its appearance from 

 the roof of the prosencephalon. The choroid plexus has also started. 



Figs. 123 and 124. Two older stages showing the increase in length of the 

 epiphysis ; its distal end is somewhat enlarged and is inserted into a concavity in 

 the cranial roof. The paraphysis is indicated at //. — The choroid plexus is con- 

 siderably increased in extent and hangs into the cavity of the fore-brain. 



