880 



SCIENCE 



[N. S. Vol. XXXVII. No. 962 



channels making up the developing thoracic 

 duct, and that finally the hemal cellular ele- 

 ments in question reach the blood stream via 

 the thoracic duct and jugular lymph sac. 

 Considering the vast number of blood cells, 

 especially erythrocytes, arising in this region 

 and the probability that they are conveyed to 

 the general circulation by the thoracic duct, 

 this duct assumes, therefore, an additional 

 phase of importance in the chick in that it 

 performs a hemophoric, or blood-carrying, 

 function. 



The view that the thoracic duct may arise 

 as detached portions of veins is in the case of 

 the chick quite untenable, since the tissue in 

 which the lymph spaces and channels arise 

 remains notably non-vascular up to the time 

 the first lymphatics appear. The writer be- 

 lieves he has sufficient evidence, soon to be 

 published, to show that the lymphatics arise as 

 isolated lacunae directly from mesenchymal 

 intercellular spaces, are not in any sense de- 

 rived from veins, and subsequently coalesce to 

 form the continuous channels of the thoracic 

 duct. 



The point recently made by other investiga- 

 tors,^ namely, that the superficial lymph plexus 

 in the region of the posterior lymph heart in 

 the chick contains stagnant blood which has 

 backed up into it from the veins, is invalid in 

 the case of the thoracic and its blood content 

 because there are no veins in this region from 

 which " backing up " could occur. 



Adam M. Miller 



a possible mea2^s of identifying the sex of 

 (+) and ( — ) races in the mucoes 

 It has been shown by the writer (1) that 

 the majority of the forms among the mucors 

 are dicecious, with the sexes separated in male 

 and female races which are capable of being 

 propagated apparently to an indefinite num- 

 ber of vegetative generations by means of 

 nonsexual spores formed in sporangia. In all 

 the dioecious species carefully investigated the 

 opposite gametes, which are produced and 

 unite to form zygospores when the two sexual 



= Clark, E. L., Aimt. Becord, Vol. 6, No. 6, 1912; 

 Clark, E. It,., Anat. Secord, Vol. 6, No. 6, 1912. 



races of a given form are grown together, do 

 not appear to diiler morphologically. Lack- 

 ing a definite criterion which an inequality of 

 the gametes would have afforded, the writer 

 has provisionally designated the opposite sexes 

 in these forms by the signs (+) and ( — ) on 

 account of a generally greater vegetative* 

 luxuriance of one sex over the other. That in 

 reality the two sexes are represented in the 

 (+) and ( — ) groups is shown by the sexual 

 reaction which may occur not only when the 

 (+) and ( — ) races of the same species are 

 grown together and perfect zygospores are 

 produced, but also by the sexual reaction which 

 may occur when (+) and ( — ) races belong- 

 ing to different species are grown together. 

 This reaction between the opposite races of 

 different species has been called imperfect 

 hybridization since it does not lead to the 

 formation of perfect hybrid zygospores, but 

 usually stops short with the formation of 

 progamates, though occasionally gametes are 

 produced which, however, never unite. 



A sexual race of a dicecious species if grown 

 between the (+) and ( — ) races of another 

 test species used as a standard, will show a 

 line of sexual reactions on one side only. 

 Some of the hermaphroditic species, on the 

 other hand, when similarly grown, show a re- 

 sponse to both (+) and ( — ) test races and 

 produce therefore 2 lines of sexual reactions. 



Some few species in the hermaphroditic 

 group are distinctly heterogamic with a con- 

 stant difference in size between the conjuga- 

 ting gametes. Figs. 1-6 in the accompanying 

 diagram will illustrate the process of conju- 

 gation in such forms. It seems reasonable to 

 consider the larger gamete female and the 

 smaller male. Upon this basis, if a sexual re- 

 action could be established between these 

 unequal gametes and the (+) and ( — ) races, 

 the race reacting with the larger female 

 gamete must be considered male, while the race 

 reacting with the smaller male gamete must 

 be considered female. 



'"Zygospore Formatioii a Sexual Process," 

 Science, N. S., 19: 864-866, 1904; "Sexual Ee- 

 production in the Mucorinese, " Proc. Am. Acad., 

 40: 205-319, pis. 1-4, 1904. 



