12 DEAN. [Vol. XI. 



employed : this had been found to give the best results of all 

 reagents the writer had used with eggs of Acipenser. 



During development the water temperature varied from 

 62°-y2° F. Hatching occurred in 200-220 hours. 



In the following table the writer records the time occupied 

 in the growth stages of Lepidosteus compared with that of Aci- 

 penser : the more rapid development of the latter was doubtless 

 due to a slightly higher mean temperature of the water as well, 

 perhaps, as to a smaller amount of food-yolk. At Delaware 

 City the mean temperature was about 68°, while that of Black 

 Lake was about 64° F. The writer has learned recently from 

 Mr. Perry that eggs of Lepidosteus deposited on June 10 

 hatched by favorable water conditions in as short a time as 

 125-130 hours. 



AFTER FERTILIZATION. {Ho^trs.) 



Lepidosteus. Acipenser. 

 First cleavage i i 



Second cleavage ......... 2 1.25 



Third cleavage ......... 3 2.30 



Blastoderm cap grows down to the level of -J- diameter of egg 32 16.30 



i " 38 24 



" f « 42 26 



I " 44 27 



Gastrulation begins ......... 37 ig 



Blastopore closes 46 58 



Embryo appears ......... 60 31 



Central nervous system outlined ...... 70 43 



Pronephic ducts appear 70 42 



Brain vesicles distinguishable 80 46 



Optic vesicles distinguishable ....... 80 46 



Embryo surrounds circumference of egg 90° (approximate) . 70 ^^ 



110° " . 85 43 



140° " .110 49 



" " " 180° « , 125 53 



" " " 200° " . 140+ 56 



" " 240° " . 146+ 61 



" " " 280° « .152+ 68 



320° " .160+ 76 



Movements of embryo first noted 149 82 



Embryo hatches 200 + 94 



Yolk material absorbed 1000 + 250 + 



