66 Heredity. 



but Adler lias verified Siebold's statement that in this 

 species parthenogenesis of the ordinary females is not 

 at all infrequent. 



Although parthenogenesis is more frequent among the 

 insects and Crustacea than it is in other animals, it is 

 not confined to these groups. 



Colin has given good reasons (Zeit. f. Wiss. Zoot, 

 xii., 1863, p. 197) for believing that among the Rotif- 

 era the summer eggs, which give rise to both males and 

 females, are parthenogenetic; while the winter eggs, 

 which hatch into females exclusively, are the only ones 

 which are fertilized. There is no reason for doubting 

 the correctness of this conclusion, but it has not been 

 placed beyond the possibility of all doubt, as is the case 

 with so many insects.. 



Many observers have thought that they have found evi- 

 dences of parthenogenesis in groups of animals where such 

 an occurrence would be very exceptional, but in most of 

 these cases there is much chance for error. Thus it has 

 been stated that the eggs of echinoderms sometimes de- 

 velop without impregnation, but when we recollect that 

 both male and female echinoderms in most cases dis- 

 charge their reproductive elements into the water, we 

 can see that it must be almost impossible to state that 

 the sea-water in which the eggs are placed contains no 

 spermatozoa of the same species. Dr. J. M. Wilson 

 has recently undertaken some experiments on this point 

 at my suggestion. He fertilized a lot of eggs from one 

 of our common sea-urchins, Strongylocentrotus, with 

 male fluid from another of a distinct genus, Arbacia. A 

 lot of Arbacia eggs were fertilized with a male Strongylo- 

 centrotus,a lot from each form with fluid from a male 

 of the same species, and eggs from each species were 

 placed in water without fertilization. 



