THE ANATOMY AND DEVELOPMENT OF PERIPATUS NOVAE-BRITANNIAE. 25 



there would hardly be occasion to speak any longer of a trophic organ. In short the 

 vesicular character of the latter is now disappearing and the trophic cavity is becoming 

 nothing else than the definitive gastral cavity. Figure 36, which also belongs essentially 

 to this stage, shows a variation in the flexure of the embryo, the head not being bent 

 under and pointing (when lying in the uterus) accurately in the direction of the vagina. 

 Moreover in this figure the trophic vesicle is more restricted than in Fig. 35, and there 

 is only a small procephalic prolongation of it which does not arch over the ventral surface 

 of the embryo. Possibly this embryo would never have gone through a stage with cephalic 

 flexure. There seems to be some latitude in the amount of flexure which it is necessary 

 for an embryo to undergo. Shortly after this stage the trophoblastic vesicle becomes quite 

 absorbed into the composition of the embryo. 



Stages XI and XII. These stages differ from one another chiefly in the amount of 

 pigment which has been deposited in the integument and it will be convenient to treat 

 them together. The full complement of legs is present and it is therefore possible to 

 determine infallibly male and female embryos. They do not differ materially in size — 

 their length, which represents approximately the length of the young at birth, averages 

 about 15 mm. — but the male embryo has 22 pairs of ambulatory appendages and the 

 female has 24 pairs. I have examined sections through such embryos for the purpose of 

 confirming the determination of sex and found the conclusion well grounded. The section 

 of an ovary, shown in Fig. 18, is from a female embryo belonging to Stage XL In the 

 male the sexual organs are also well differentiated and the pvgidial bulbus appears even 

 more pronounced relatively than in a mature male. 



In the two oldest embryos which I obtained (belonging therefore to Stage XII) the 

 antennae and entire dorsal surface were darkly pigmented but the ventral surface was 

 on the whole unpigmented. The head and neck were bent under the abdomen, the 

 2nd leg lying in the bend. The antennae in one were stretched out along the abdomen 

 and in the other were bent back under the head. These embryos were taken from one 

 female and were lying in the terminal portions of the uteri next to the vagina. I have 

 never found a darkly pigmented embryo in any other portion of the uterus than this, 

 but I have found an unpigmented embryo in this position. 



From the same female from which these embryos were taken, the embryos following 

 them belonged, in accordance with the successional mode of development followed by 

 this species, to Stage XL The antennae were pigmented as in Stage XII but the 

 dorsal surface was only very faintly pigmented, the general colour effect being whitish 

 with faint greenish tinge. 



Although in all extensive collections of Peripatus which have been made, as well 

 as in my own, the males are much less numerous than the females, yet, singular to say, 

 the two oldest embryos in each of the two females which I opened first, were all four of 

 them males, and three of the embryos immediately following upon these respectively were 

 females. The fourth was probably a female but I could not count the number of its 

 appendages. This order may be a mere coincidence but at first sight it suggests a 

 periodicity in the production of males and females and any future observer of this species 

 should pay attention to this matter. 



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