340 



SCIENCE 



[N. S. Vol. XXXVII. No. 948 



show a variation from the general law of de- 

 creasing basicity for plutonic intrusions, but 

 this may be explained by the localized char- 

 acter of the phenomena. 



C. A. Stewart 



UNn^ERSITY OF IDAHO 



FERTILIZATION AND EGG-LAYING IN MICROCOTYLE 

 STENOTOMI 



Although the process of fertilization of the 

 ovum is readily visible in those animals in 

 which these elements meet outside the body in 

 water, the actual behavior of the internal 

 organs in those other animals where the proc- 

 ess occurs within the body is seldom seen. It 

 is for that reason that it seems desirable to 

 describe it as studied in the transparent 

 Microcotyle Stenotomi. 



Copulation has been carefully observed and 

 graphically described by ZeUer in the case of 

 Polystomum integerrimum, where the two 

 vaginal orifices are at the lateral margins, but 

 no other description has been found in the 

 literature on the monogenetic trematodes, and 

 in the case of the microcotylinae is of special 

 interest, since although hermaphrodites they 

 can hardly carry out mutual copulation at the 

 same time, as the vaginal orifice is median 

 and dorsal while the penis is protruded from 

 the ventral side. 



Microcotyle Stenotomi, which occurs on the 

 gills of Stenotomus Chrysops, is small enough 

 (2.5 mm.) to become quite transparent when 

 slightly compressed by the coverslip. If a 

 number of these worms be placed alive in a 

 watchglass full of sea water some of them will 

 be seen to go into conjugation after certain 

 repeated preliminary touching together of the 

 anterior ends of the two bodies has taken 

 place. In this passing of the anterior part 

 of the body of one over that of the other the 

 greatest acuteness of sensation is shown. 

 However, after a certain amount of friction 

 together, one worm almost spasmodically be- 

 comes fastened by its anterior ventral end, 

 where the genital pore is situated, to the cor- 

 responding portion of the dorsal surface of 

 the other in the position of the vaginal open- 

 ing. They are therefore clasped together by 



the anterior ends, almost at right angles to 

 one another, while still supporting themselves 

 on their footlike sucker discs. Because the 

 cirrus and surrounding genital aperture are 

 generally provided with clusters of small hooks 

 the pair is enabled to keep their position dur- 

 ing the act. 



The spermatozoa pass through the Y-shaped 

 reservoir of the vitellaria to be stored in the 

 seminal reservoir or spermatheca, whence it is 

 ejected as required. A similar provision ex- 

 ists, as is well known, in many animals of 

 more complete development. 



In order to follow the later stages in the 

 process of fertilization the worm must be put 

 in a drop of sea water under the coverslip 

 with a hair beside it to prevent too great 

 crushing by the weight of the coverglass, and 

 to allow of the normal movements of the geni- 

 talia. Anteriorly and ventrally'is the genital 

 pore through which the uterus opens. On the 

 dorsal surface somewhat behind this is the 

 orifice of the vagina. The ovary is a con- 

 voluted tube filled with ova which runs across 

 the middle of the body, turning backward to 

 end in an oviduct, while on each side of the 

 body, occupying most of its cavity, is the 

 vitellarium, giving off ducts which unite in 

 a Y-shaped reservoir in the midline behind 

 the ovary. Testes are present in a great 

 group in the midpart of the body toward the 

 caudal end. 



In the ovary the ova are immature at the 

 end of the organ, which is turned to the right ; 

 toward the other end, as the oviduct is ap- 

 proached, they become larger and mature. 

 The oviduct may be seen proceeding toward 

 the tip of the Y-shaped vitelline reservoir. 

 Before reaching this it is joined by the duct 

 of a small muscular sac which in this case is 

 kidney-shaped and which is the seminal reser- 

 voir. If one is fortunate enough to see an 

 ovum leave the ovary on its way toward the 

 uterus, one can also observe that the seminal 

 reservoir contracts spasmodically and injects 

 a fine jet of opaline fluid into the oviduct 

 toward the oncoming ovum, which on meeting 

 the spermatozoa quickens its motion. It re- 

 cedes a little, then advances again four or five 



