482 THOMAS n. BRYCR. 



on spontfincons parthenogenesis. In confirmation of Fol, lie 

 found that eggs from fully-matured animals did not segment 

 spontaneously^ but only after a considerable time underwent 

 changes considered pathological. The nucleus enlarged 

 more and more, and after ten to fifteen hours the esrars 

 died and fragmented. Only among hundreds of eggs here 

 and there one had divided into two. At Trieste, however, 

 in a season when the animals were late in maturing, and at a 

 time when males were rarely got, he observed in a limited 

 number of cases (in Astcrias glacialis, and Astero 

 pecten) that after the polar mitosis had occurred, the nucleus 

 did not come to rest, but continued to divide. There resulted 

 an irregular division, but here and there a blastula was found 

 which had no vitelline membrane. Into the interesting 

 observations and suggestions regarding the failure of the 

 second polar body extrusion, and the union of two vesicular 

 nuclei in the egg, we cannot here enter. The main point 

 established was, that fully-matured eggs did not develop 

 parthenogenetically, but that in some few cases immature 

 eggs did divide irregularly, and in a small number of cases 

 blastulee were formed. A number of observers have 

 described the occurrence of natural parthenogenesis in 

 Echinoderms, and it is an open question ; but apart from its 

 possible relation to immaturity of the ovum, the sources of 

 error in the matter of infection by spermatozoa are so many, 

 and the causes which artificially start parthenogenetic 

 development in certain cases are so slight, that all cases of 

 so-called '' natural parthenogenesis " arc open to suspicion, 

 but even granting that it may occur, it is a matter of no great 

 moment in the question of " artificial parthenogenesis." It 

 would be only additional evidence of the fact, that there is in 

 these forms a tendency to parthenogenetic development, 

 which, however, does not normally occur. 



Mitotic division may be excited in unfertilised eggs in a 

 variety of ways. 



First, by increasing the degree of concentration of the 

 sea water (Morgan, Hunter), or by increasing the osmotic 



