226 



SCIENCE 



[N. S. Vol. LIII. No. 1367 



GENERAL OUTLOOK 



As the result of a more general recognition 

 of the basic importance of mineralogy in pure 

 and applied science and in various branches of 

 industry, and with a national society boasting 

 of a membership including the progressive in- 

 vestigators and devotees of the subject, and 

 with a well established and widely recognized 

 official monthly publication, the future of 

 mineralogy in America is assured. The prob- 

 lems of really fundamental significance re- 

 quiring a -com-prehensive knowledge of crystal- 

 lography and mineralogy are indeed many. 

 The applications of the methods and truths of 

 our science are constantly increasing and if 

 America is to assume leadership in this great 

 field it can be most speedily and advantage- 

 ously accomplished through the friendly co- 

 operation of the members of an organization 

 such as this. 



Edward H. Kraus 



. MlNERAiOGICAL IlABORATORY. 

 UNrVEKSITT OF MICHIGAN 



SEX IN THE TREMATODE FAMILY 

 SCHISTOSOMID.ffii 



The trematode family Schistosomids in ad- 

 dition to containing three species which pro- 

 duce important human diseases, viz.. Schisto- 

 soma hwmatohium, 8. mansoni, and S. japon- 

 icum, is interesting because it is the only 

 group of the trematodes in which the sexes 

 are separate in the adult stage, which lives 

 in the vertebrate. In this stage there is an 

 extreme sexual dimorphism, the structure of 

 the male being adapted for grasping the 

 female in the gynsecophoric canal during 

 copulation and the female having a very long 

 slender body. The complete life cycles of the 

 three human species of tliis family have been 

 worked out in the last seven years, making it 

 now possible to attack the problems related to 

 the determination of sex and the development 

 of sexual dimorphism. 



Just what is involved in these problems can 



1 From the department of medical zoology of the 

 school of hygiene and public health of the Johns 

 Hopkins University. 



perhaps be made clear by a brief outline of 

 the life cycle of one of the human species of 

 this family. Schistosoma japonicum,. The 

 adult of this species lives in the bloodvessels 

 of the liver and mesenteries of man and other 

 mammals in the far East. The adults are 

 almost always found in copulation in the 

 vessels of the hepatic portal system. The 

 fertilized ovum develops into the miracidium 

 within the egg shell before the egg escapes 

 from the host. The miracidium hatches 

 almost immediately when the egg is voided 

 into the water and dies within a short time 

 unless it comes in contact with a small 

 species of snail, Blanfordia nosophora (Eob- 

 son). It penetrates vigorously into this snail 

 and metamorphoses into a sac-like structure 

 known as the mother sporocyst. The germ 

 cells of the miracidium are carried over 

 directly into the mother sporocyst and develop 

 by parthenogenesis into daughter sporocysts. 

 A single mother sporocyst may live for a con- 

 siderable period of time and produce several 

 hundred daughter sporocysts. These daughter 

 sporocysts also carry germ cells and produce 

 by parthenogenesis cercarise which are the 

 larvae of the dioecious vertebrate-dwelling 

 adults. These cercarise escape into the water 

 and will penetrate directly through the skin 

 of any suitable host with which they come 

 in contact. From the skin they make their 

 way to the blood vessels of the liver, where 

 they develop to sexual maturity in about three 

 to four weeks. In fact I have seen copulation 

 in an experimentally infested mouse nineteen 

 days after exposure to these cercarise. 



The first question which naturally arises in 

 connection with the sex phenomena in this 

 life cycle is how far back can the sexual 

 dimorphism be traced in the development of 

 the adult from the eercaria in the final host. 

 In a recent series of studies on the develop- 

 ment of Schistosoma japonicum, in experi- 

 mentally infested mice I have been able to 

 distinguish males from females in specimens 

 about 0.3 mm. in length. Since the body of 

 the eercaria of this species is about 0.15 mm. 

 to 0.20 mm . in length and the smallest 

 sexually mature forms have a length of about 



