592 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



being found in the lack of contemporaneousness in the original fertilization and 

 the halting of the developmental processes at definite periods. 



The morphological features of the young of the Echinus male X Echinus female 

 and the Antedon male X Echinus female crosses are exactly the same. Mesenchyme 

 formation begins in the blastula stage in contrast to the conditions in Antedon, 

 where there is no primary mesenchyme, and in the grouping of the mesenchyme 

 elements there is no difference between the hybrids and the pure-bred animals. 



After the mesenchyme has become divided into two masses, and the archen- 

 teron has formed in the manner characteristic of Echinus, the beginnings of the 

 three-rayed skeleton appear. The plutei, which exhibit the arms characteristic 

 of the plutei of Echinus, often live for several days. 



It is noticeable that, although there occur periods of arrested development 

 or deviations in the formation of certain organs, similar abnormalities occur in 

 the development of pure-bred Echinus. Godlewski never found a deviation from 

 the normal type of the mother animal which could be considered as resulting from 

 the influence of the male parent. 



From these observations it follows that fertilization and the transference of 

 characters are two quite unrelated processes. The spermatozoa can penetrate the 

 egg, and its nucleus can unite with the egg nucleus, but in spite of the union 

 of the nuclei none of the characters of the male parent appear in the morphological 

 structure of the hybrid. 



His success in fertilizing echinoid eggs with comatulid spermatozoa led God- 

 lewski to try fertilizing fragments of echinoid eggs from which nuclei were absent 

 with Antedon spermatozoa. 



A small percentage of such egg fragments were fertilized. Development 

 began with cleavage, which presented the usual type of merogonic echinoid 

 division. Often the eggs died during the cleavage stages, but some developed 

 to blastulse, and Godlewski obtained four embryos which had reached the gas- 

 trula stage, though in none of the four were there any traces of the beginnings 

 of the skeleton. 



In none of the embryos was there the slightest trace of any Antedon char- 

 acters ; the development was invariably that of the Echinus embryo. 



ASYMMETRY. 



In the great majority of the comatulids the body is almost perfectly pen- 

 tamerous, being composed of five similar sectors. The presence of a small 

 muscular cone in the slightly enlarged posterior interradius, at the summit of 

 which is the posterior opening of the spiral digestive tube, gives the only indication 

 visible externally of a departure from true pentamerous symmetry. Internally the 

 contents of the visceral mass, especially the coiled digestive tube and the excentric 

 axial organ, are unsymmetrical, but the nerves and the skeleton and the more super- 

 ficial organs centering in ring systems about the mouth are perfectly pentamerous. 



In certain types, however, a more or less marked deviation from the charac- 

 teristic symmetry occurs. 



In many of the Comasteridse the mouth moves anteriorly to a position at the 

 base of the anterior ray, and then to the right to a position between the bases of 



