484 SUMMARY OF CURRENT RESEARCHES RELATING TO 



marks of mutation ; and that it is hereditary in a strong though variable 

 degree throughout the parthenogenetic series. 



In several respects variation in this Rotifer appears like a species- 

 making process. The different types produced occur erratically, though 

 sometimes abundantly, in nature ; their differences would he quite suffi- 

 cient for specific distinction, and several of the forms produced closely 

 parallel types of the genus which have been assumed to be definite 

 species. But unless the variation affects the sexual gametes, it is not 

 akin to species-making, and at first sight it seems that all the fertilized 

 or resting eggs hatch as individuals of the small saccate type, which 

 represents in general the primitive phylogenetic form of the entire 

 genus. The astonishing variations of the parthenogenetic series, germinal 

 though they are, thus seem to be wiped out by sexual reproduction, much 

 as the somatic modifications of the complex Metazoan are wiped out by 

 the same process. 



"What the authors have sought to discover is whether the wiping-out 

 process is complete ; whether the fertilized egg is so different a thing 

 from the parthenogenetic egg ; whether the entire variation of the 

 species, and doubtless of the genus as a whole, is but the play of the 

 environment upon parthenogenesis as such, or whether it is the result of 

 the forces fundamentally modifying the gametic constitution of the 

 species. The first generation of young from the fertilized egg is always 

 structurally the same from whatever type of the species the egg is 

 derived, but it is possible that the young saccate individuals derived 

 from different eggs differ physiologically and in their reproductive 

 tendencies. The inheritance through the fertilized egg need not mani- 

 fest itself in the visible characters of the individual which emerges from 

 this egg ; it may be hidden as tendencies only to manifest itself in later 

 generations. 



The general conclusion reached is that germinal changes (induced by 

 peculiarities in nutrition) may be transmitted through sexual as well as 

 through parthenogenetic generations. It is a remarkable fact that a 

 certain type or form when once induced (the humped form of A. amphora) 

 may in reality be transmitted with full force despite an interruption of 

 one or more generations in which this form is not expressed. Although 

 the conditions are totally different, the phenomenon suggests that of 

 recessive and dominant characters. The authors have also found that 

 the union of gametes has little, if any, influence on the vitality or vari- 

 ability of the Asplanchna stock. 



Echinoderma. 



Larva of Porania pulvillus.*— James F. Gemmill describes a 

 feeding brachiolarian stage in the life-history of this Phanerozonate 

 Asteroid, which shows that the division into Phanerozonia and Crypto- 

 zonia is not necessarily associated with fundamental differences in 

 development. The blastula formation is by egression of central cells in 

 lines appearing externally as surface furrows. There is a practically 



* Quart. Journ. Micr. Sci., lxi. (1915) pp. 27-50 (2 pis.). 



