HYBRIDS BETWEEN FUNDULUS AND MACKEREL 395 



The hybrid situation in Teleosts as compared with that in Echinoids 



Taxonomically the group Teleostei is of lower value than the 

 group Echinoidea, the former being merely an order of the sub- 

 class Teleostomi of the class Pisces, while the latter is a class on 

 a par with the class Pisces. A group of Echinoidea correlative 

 with the order Teleostei is the order Diademoida of the sub- 

 class Regularia. A strict comparison of hybrid phenomena 

 would therefore be limited within the confines of these two 

 orders, Diademoida and Teleostei. As a matter of fact, only 

 one Echinoid cross has been made that exceeds the limits of the 

 Diademoida. 



No one has as yet succeeded in crossing a Teleost with any of 

 the Ganoid orders of Teleostomi nor with any other subclass of 

 Pisces, much less with members of other classes of vertebrates 

 or with invertebrate phyla. By the use of appropriate chemicals 

 it might conceivably be possible to inseminate Teleost eggs with 

 other than Teleost sperm, but my impression is that the micro- 

 pyle would be too much of an obstacle for a type of sperm very 

 different from that of a Teleost. Even if a foreign spermatozoon 

 could be forced past the micropyle barrier, it would doubtless 

 be unable to initiate development for the same reasons that the 

 several sorts of parthenogenetic agents, that have been extensively 

 tried upon Teleost eggs, have failed to bring about any develop- 

 mental result; for Teleost eggs, unlike Echinoid eggs, are extreme- 

 ly refractory to parthenogenetic agents and would therefore 

 probably fail to respond to foreign sperm. Hybridization ex- 

 periments among Teleosts are, therefore, confined entirely within 

 the order and at most will be of subordinal width. A very large 

 number of crosses of subordinal, of family, and of generic width 

 have been made. A companion of the following table (table 2) , 

 which represents the classification of the genera of Teleosts, 

 with table 1 will be of interest. 



A survey of this table shows that nearly half of the genera used 

 are members of the large suborder Acanthopterygii, just as most 

 of the Echinoid genera used in crosses belong to the suborder 

 Echinina. The four suborders in the table have been crossed in 

 a great many ways and with varying degrees of success. At 



