BULLETIN 351^ U. S. DEPARTMENT OF AGRICULTURE. 



THE EMBRYO. 



The terrapin scale is viviparous. Authors making reference in 

 literature to the eggs of this insect undoubtedly referred to the 

 embryos, which probably were mistaken for eggs. Undeveloped eggs 

 are present in some specimens in the fall before hibernation. Dis- 

 sections made September 9, 1913, showed a pair of very small race- 

 mose ovaries containing a few undeveloped eggs located to the right 

 and left of the alimentary canal, and a small, globular, brown- 

 colored receptaculum seminis attached to the vagina. Dr. Quain- 

 tance has observed eggs in hibernating females from Winchester, 

 Va., as early as Jan.uary 19. The writer has taken rudimentary eggs 

 at various times during the hibernating period. With the renewal 

 of growth in the spring there is a rapid increase in both the number 

 and size of the eggs. The average size of four embryos at birth was 

 as follows: Length, 0.3437 mm.; width, 0.1625 mm. 



The data in Table II were taken from the largest embryos obtained 

 at each dissection. Some of these were nearly full size by May 16, 

 although it was not until the first week in June that the eyespots 

 and segments became prominent. 



Table II. 



Measurements of developing embryos of the terrapin scale, taken by dissection, 

 191S. 



Date. 



Number 

 of speci- 

 mens. 



Average 

 length. 



Average 

 diame- 

 ter. 





Mm. 



Mm. 



5 



0. 2986 



0. 1754 



4 



.3343 



.1781 



5 



.32 



.184 



5 



.344 



.173 



5 



.346 



.1625 



4 



.3437 



.1625 



Locality. 



May 10- 

 16. 

 17. 

 23- 

 27. 



June 28 



Moht Alto, Pa. 



Do. 



Do. 



Do. 

 Midvale, Pa. 

 Mont Alto, Pa. 



1 Measured at birth. 



The ovaries remain active and continue to produce eggs as long 

 as nutriment is supphed to them. They are among the last organs 

 of the scale to disintegrate. 



Table III gives data from dissections during the spring of 1912 

 and 1913. These counts show that most of the embryos are formed 

 before the end of May. The greatest number found was 881 on 

 June 4, 1913, and the ovaries of the parent scale were still active. 

 It is evident from this that vigorous females may produce as many 

 as 900 embryos. The oldest embryos are far advanced by June 6, 

 and they are mature by June 15, at which time the eyes, the appen- 

 dages, and the abdominal segments were clearly seen thi'ough the 

 membrane. 



