. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 192 ANTHONY E. GANAROS about ° C. (Table I). However, since the rate of development was faster at ° C. and the difference in the percentage survival of egg cases producing young conchs between ° C. and ° C. was small, it was considered possible that the optimum was above ° C. Therefore, a second experiment was conducted at ° C. and ° C., using 20 egg cases in each temperature group, and the percentage survival of ova determined. At ° C., 139 out of 176 ova, or per cent, developed to the p
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 192 ANTHONY E. GANAROS about ° C. (Table I). However, since the rate of development was faster at ° C. and the difference in the percentage survival of egg cases producing young conchs between ° C. and ° C. was small, it was considered possible that the optimum was above ° C. Therefore, a second experiment was conducted at ° C. and ° C., using 20 egg cases in each temperature group, and the percentage survival of ova determined. At ° C., 139 out of 176 ova, or per cent, developed to the protoconch stage, as compared to 96 out of 168 ova, or per cent development, at ° C. Thus, although the rate of development was faster at ° the optimum temperature, from the standpoint of successful development to the young conch stage, appeared to be about ° C. Moreover, at ° C. the period for protoconch release was shorter than at any other FIGURE 4. Egg case, with outer membrane removed, containing three early protoconch larvae which show partial spiral development and pigmentation. Note also the two undeveloped ova in the same egg case. X 10. Since the egg cases in the first experiment were deposited within a period of three days, their age alone could not account for the difference of 13 to 22 days between the release of the first and last young conch. The conclusion that slight differences in the age of the cases are not responsible for pronounced differences in the time needed for release of young conchs of the same groups is further substan- tiated by our second experiment at ° C. in which egg cases collected within a 16-hour period started releasing young conchs at 62 days and continued to do so for 19 days. TOLERANCE TO Low TEMPERATURES To study the tolerance of egg cases to winter temperatures when exposed at low tide and to simulate tide pool conditions, cases containing ova and veligers were placed in water and
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