Hyhridizaiion of Ec/iwoids. 33 



In group (2) I included such cases as result from the activations 

 of the Echinoid egg by the sperm of annelids and mollusks (Godlewski, 

 1911; Kupelwieser, 1906) and the fertilization of eggs which had been 

 given a certain impulse to parthenogenetic development by means 

 of chemicals, which give, as these authors have pointed out, thely- 

 karyotic larvse. I stated further that, practically, larvae derived from 

 such crosses inherit from the egg parent alone just as strictly as if the 

 eggs had been caused to develop from the first by artificial chemical 

 fertihzation. They are false hybrids. 



0^26 



^ "At J 



25 



^A 5/ n ^_27 



28 A » 



Fig. 25, Cidaris 9 X Tripneuslesd'. Median section of three, other two not shown, 



showing cliroinosomes becoming transformed to chromosomal vesicles before 



contraction of chromosome has taken place. X 2,400. 

 Fig. 26, Parthenogenetic Cidaris egg. Prophase of monaster division. X 2,400. 

 FiQ. 27, a and 6, Parthenogenetic Cidaris egg. Two successive sections of monaster plate. 



Many elements shown in b are sections of those shown in a. X 2,400. 

 Fia. 28, Parthenogenetic Cidaris egg. Monaster division. All chromosomes have divided; 



18 pairs. X 2,400. 



These Cidaris-LytecJiinus and Cidaris-Triprieustes crosses consid- 

 ered in this paper constitute another group. 



(6) Elimination of part of the chromosomes, presumably paternal and failure 

 in development. 



These may be regarded as partial hybrids. Probably several 

 additional crosses that have been made, but which have not received 

 adequate cytological examination, will ultimately be found to belong 

 in this group. 



In these crosses, development seems to proceed well as long as the 

 generalized type of development, common to each, continues; devel- 

 opmental block occurs when the period of specialized development 

 begins. The egg seems unable to accommodate itself fully to the 

 impulse for a divergent type. 



