8 BULLETIN 351, U. S. DEPARTMENT OF AGRICULTURE. 



BIRTH OF THE TERRAPIN SCALE, AS OBSERVED AT MONT ALTO, PA., IN 1913. 



The following data were obtained by observing 50 scales which 

 gave birth to 3 ; 000 young during the period of 4 days, June 22 to 

 June 26, 1913: 



The young are brought forth as embryos, usually inside of a sac or 

 amniotic membrane. The vaginal passage of the mother offers con- 

 siderable resistance to the passage of the first young of the season, as 

 they are very turgid or swollen, and the amniotic sac is nearly always 

 ruptured, allowing the embryo to escape. This is the only time when 

 they are born free, as later in the season the embryonic sac comes 

 through unbroken. Toward the end of the season the larva?, after 

 birth, may remain as long as 8 minutes in the embryonic membrane, 

 but the time is seldom more than 4 minutes. The embryos have an 

 average length of 0.36 mm., and a transverse diameter averaging 0.18 

 mm. (PI. I, fig. 1,6.) 



The structure of the larva shows through the amniotic membrane. 

 The antennas are folded downward and lie parallel along the ventral 

 surface. The proboscis lies between the antennas and extends along 

 the midventral line for three-fourths of the length of the body. The 

 legs lie alongside the antennae and extend beyond them to near the 

 posterior end of the body. The major apical setae and the anal plates 

 are folded forward upon the ventral surface of the body. The eyes 

 show prominently through the membrane. The sides of the body are 

 rolled slightly inward, so as nearly to enfold the ventral appendages. 

 When the embryonic membrane bursts the young appears as a wet, 

 flat larva, which remains motionless for a few minutes, during which 

 the body unfolds and the appendages assume their normal position. 

 The cast membranes of the numerous progeny remain and form a 

 deposit on the floor of the brood chamber. (PL I, fig. 1,0,.) Twenty 

 minutes after birth the larvae have assumed their characteristic 

 flatness and are moving about in the brood chamber, where they 

 remain usually until the following day, or even longer if unfavorable 

 weather conditions prevail. 



Observations of birth are difficult. The displacement necessary for 

 observing this operation loosens the feeding tube and so deprives the 

 parent of the needed nutriment. It is, therefore, impractical to 

 make observations covering an extended interval. 



At the beginning of reproduction the time between births may be 

 as short as 2 minutes. As the exhaustion of the parent increases the 

 interval between births becomes longer, until by the thirtieth day 

 birth has practically stopped. 



Table V gives birth data for 7 larvae from well-exhausted parents, 

 under favorable conditions. It shows an average interval between 

 births of 8.5 minutes and the average time per birth as 2.43 minutes. 

 These birth data can be taken as a good average for the major part 



