204 SUMMAEY OF CURRENT RESEARCHES RELATING TO 



confined to the mesoplankton, and some are only met with there in an 

 adult state after having passed I he earlier stages of their development in 

 jthe epiplankton of warmer regions. This great difference in the number 

 of species between epiplankton and mesoplankton is characteristic of the 

 temperate zone. In tropical and subtropical regions the Chastognatha 

 of the surface are much more multifarious owing to the presence of 

 numerous epiplanktonic warm-water species, while those of the lower 

 layers, in consequence of the cosmopolitanism of most (perhaps all) of 

 the mesoplanktonic species, scarcely change. 



West Indian Chsetognatha.* — Rudolf v. Ritter-Zahony reports on 

 a collection from the Tortugas, including Sagitta helcnse sp. n., and 

 numerous previously known species. The collection supports the con- 

 clusion that the distribution of the epiplanktonic warm-water species is 

 not localized, but extends round the earth in zones bounded to north 

 and south by isotherms. 



Theory of Dwarf Males in Myzostoma. t — A. F. Coventry applies 

 <i. W. Smith's theory of the dwarf males in barnacles to Myzostoma. 

 The theory is that secondary hermaphroditism has been imposed on a 

 primitive dicecism, on the males. Ordinary monoecious Cirripedes are 

 really males, all the females having been suppressed. The complemental 

 males are* in an arrested state of development due to the condition of 

 protandric hermaphroditism through which they at one time passed. In 

 Rhizocephala, the dwarf males never become sexually mature, being 

 represented by the Cypris larvse found on the young SaccuUna externa. 

 Smith believes that these Cypris larvae and the complemental males of 

 the Pedunculata are potential hermaphrodites, arrested by the position 

 taken up by them on fully developed individuals. In Epicarida, all 

 individuals are at first larval males, which, after crawling upon the adult 

 (functionally female) individuals and fertilizing them, migrate to and 

 become parasitic on various Crustaceans, and there assume the female 

 condition. Coventry points out that the facts known about Myzostoma 

 seem to be susceptible of a similar interpretation to that suggested by 

 Smith for Cirripedes. 



Nematoh.elminth.es. 



[ Idiochromosomes in Ascaris.J — C. L. Edwards finds evidence of a 

 distinct idiochromosome in Ascaris megalocephala. One half of the 

 spermatozoa contain the two well-known rod-shaped elements, while the 

 remaining spermatozoa possess, in addition to the two large chromo- 

 somes, the small heterotropic idiochromosome. In a univalens worm he 

 found a number of equatorial plates of the first cleavage division which 

 showed an unpaired idiochromosome. 



In Ascaris lumbricoides the sex-determinant is in the form of five 

 univalent idiochromosomes. Some of the spermatozoa have simply 

 li) chromosomes, and these fertilizing ova with 24 (including 5 idio- 



* Zool. Jahrb. (1910), Supplement xi., Heft 2, pp. 133-14 (1 pi.). 



t Ann. Nat. Hist., v. (1910) pp. 378-80. 



% Archiv f. Zellforsch., v. (1910) pp. 422-9 (2 pis.). 



