. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. NATURAL HISTORY OF CUMINGIA TKLLINOIDKS. 213 been able to recognize the older larva?. The chief difference that I have observed between the young veligers of various lamellibranchs is in their general appearance. Some have a thicker shell than others and therefore refract light differently. As is well known the veligers of all lamellibranchs are so much alike that they can be distinguished, if at all, only by experts. The differences are largely indefinable and are apparent only after long study. TABLE II. SCHEDULE OF DEVELO
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. NATURAL HISTORY OF CUMINGIA TKLLINOIDKS. 213 been able to recognize the older larva?. The chief difference that I have observed between the young veligers of various lamellibranchs is in their general appearance. Some have a thicker shell than others and therefore refract light differently. As is well known the veligers of all lamellibranchs are so much alike that they can be distinguished, if at all, only by experts. The differences are largely indefinable and are apparent only after long study. TABLE II. SCHEDULE OF DEVELOPMENT AT HIGHER SUMMER TEMPERATURES, 22°-23° C. First polar body 7 to 9 minutes Second polar body 27 to 30 First cleavage 45 to 50 Second cleavage 70 to 75 Eggs developing at the rate shown in Table II. may reach the complete veliger stage in from twenty-four to thirty hours. The rate of development which Morgan gives for Cumingia trochophores and veligers is considerably too slow, and his statement that unfertilized centrifuged eggs are intact after forty-eight hours is also erroneous. Unfertilized eggs fragment within twenty-four hours. It should be noted, however, that he was not particularly concerned with the rate of development and these oversights do not affect the validity of the conclusions he draws. TABLE III. MEASUREMENTS AT VARIOUS AGES. Egg .061 to .065 mm.—average .062 to .063. Blastula same as above. Trochophore same as above but slightly elongated anteroposteriorly. Two day veliger .074 x .090 x .055 mm. to .08 x .091 x .055 mm. Ten day veliger .09 x .10 mm. Two weeks veliger .095 x .105 mm. Three weeks Cumingia metamorphosed .09 x .105 mm. to .097 x .155 mm. Four to five months (size attained before first winter.), 6 x 5 mm. to io x 8 mm. One year, n x 8 mm. to 13 x 9 mm. (sexually mature). Two years, 14 x n mm. to 16 x n mm. Three years, 17 x 12 mm. to 17 x 13 mm. Four years, 18x12 mm. to x 14 mm. (Largest specimens found). Experiments are in progress
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
