776 



SCIENCE 



[N. S. Vol. XXV. No. 646 



mid ventral radial canal on the fourth day 

 and, after hatching on the sixth day, de- 

 velops a sucker. On the ninth day a 

 second pedicel arises to the left from the 

 mid ventral radius. Only two pedicels are 

 found until the twenty-second day when a 

 third appears also to the left of the mid 

 ventral radius. On the twenty-fourth day 

 buds of the first pair of papilla ventrad 

 from the anterior ends of the dorsal radii 

 inaugurate the bilateral symmetry later 

 shown in the appendages. On the thir- 

 tieth day the fourth pedicel, again to the 

 left, arises from the mid ventral radius 

 and also one bud ventrad from both right 

 and left ventral radii. Not until the 

 fortieth day does the first pedicel arise to 

 the right from the mid ventral radius. On 

 the fifty-third day the second pair of 

 papillae arises ventrad from toward the 

 posterior ends of the dorsal radii. At this 

 time twenty pedicels and nineteen buds 

 have appeared from the ventral radii and 

 nine papillse and twenty-seven buds from 

 the dorsal. The seventy-fifth day in my 

 series from the embryos presents the 

 largest number of appendages, forty de- 

 veloped and forty-five buds. Four of the 

 smallest adults from my statistical series 

 have 77, 99, 141 and 150 appendages and 

 twenty, the adult number, of tentacles. 



Some Further Points in the Development 

 of Ophiothrix fragilis: E. W. MacBride, 

 M.A., F.R.S., McGill University. 

 In December, 1903, the author read a 

 paper at the Philadelphia meeting of the 

 American zoologists on the early stages in 

 the development of the British ophiuroid, 

 Ophiothrix fragilis. Since that time he 

 has been continuously engaged in working 

 out the development completely and hopes 

 to be able to publish an exhaustive account 

 of it this summer. Meanwhile some inter- 

 esting points have transpired. In the 

 former paper on the subject the segmenta- 



tion was described as leading to the forma- 

 tion of a morula. An invagination on one 

 side gave origin to the archenteron, the 

 invaginated cells not forming a simple 

 vesicle but a sac with a solid tongue pro- 

 jecting from one side of it. From the apex 

 of the archenteron the coelom arose as a 

 vesicle, and the embryo became triangular 

 in shape— one point being posterior and 

 the two others the rudiments of the first 

 arms of the ophiopluteus larva. The in- 

 terior cells of the morula gave rise to the 

 mesenchyme from which the skeleton of 

 these arms was developed. A subsequent 

 visit to PlymoiJth and renewed experi- 

 ments in artificial fertilization led to the 

 unexpected result that the tjrpe of develop- 

 ment previously described was that of 

 eggs which were not quite ripe. When a 

 male and female were enclosed in a glass 

 jar and allowed to spawn naturally the 

 segmentation of the egg led to the forma- 

 tion of a hollow blastula one side of which 

 became thickened and gave rise to mesen- 

 chyme. Regular invagination followed 

 giving rise to a normal archenteron en- 

 tirely devoid of any such tongue as was 

 described above, the coelom arose as a thin- 

 walled vesicle which became completely 

 separated from the archenteron before 

 dividing into right and left halves. At 

 the opposite pole of the larva to the 

 blastopore there was developed a great 

 crest of vacuolated cells, probably an ap- 

 paratus to assist in flotation. This crest 

 disappeared as the first two arms of the 

 larva became larger. It follows, then, 

 that it is not a certain test of the ripeness 

 of an egg that it can be fertilized, and that 

 a small change in the chemical condition 

 of the egg can effect a great change in the 

 subsequent development. 



The later development of the larva is in- 

 teresting on account of the history of the 

 ccelom. This becomes divided on both left 

 and right sides into anterior and posterior 



