196 AMPHICARYON ACAULE. 



Chun, the larger nectophore entirely encloses the smaller, and there is no reason 

 to suppose that with further growth this condition may not be attained in the 

 Pacific specimens. In earlier stages in growth the smaller nectophore, as Chun 

 observed, is proportionately much larger. In our smallest individual it is plano- 

 convex, nearly circular, and considerably overlaps the larger nearly spherical 

 nectophore. At this stage there is no distinct hydroecium, but with advancing 

 growth the larger nectophore becomes deeply, the smaller one slightly concave 

 along the ventral surface, so that in the older stages (Plate 4, fig. 1) there is a 

 well-developed hydroecial tube extending from end to end of the smaller necto- 

 phore. The nectosac of the larger nectophore is of the usual type; it reaches 

 to about the mid-level of the nectophore, is narrow and cylindrical in form, and 

 its canals pursue a direct course suggesting the condition among Diphyids 

 rather than the convolutions which they follow in the Prayinae. But, as noted 

 above (p. 195), the corresponding structure in the smaller nectophore is very 

 much reduced. In large specimens it is extremely small (Chun, '88, p. 1163); 

 but even here the four radial canals can easily be traced (Plate 4, fig. 4). Appar- 

 ently the bell-mouth is permanently closed; at least I have seen no evidence, 

 other than a slight indentation of the surface of the nectophore, to indicate that 

 it could be opened in life. In the younger stages the nectosac is relatively larger 

 (Plate 4, fig. 8), but its opening is as tightly closed. Indeed so degenerate is 

 it even at this stage that it is doubtful whether it ever functions as a swimming 

 bell. If we judged from the adult only, and from analogy with the other 

 Prayinae, we should expect the enclosed nectophore to be the younger; but 

 its relatively larger size in younger stages, when it overlaps the nectophore 

 which later encloses it, and its subsequent relative degeneration, shows that it 

 is in reality the older, and that the younger overtakes it by its much more 

 rapid growth. 



Stem and appendages. The stem is so short that Chun ('88, p. 1162) speaks 

 of it as "zu einer Scheibe umgebildet." In none of the specimens studied is 

 it extended any further than in the figure (Plate 4, fig. 1, 3). The character- 

 istic form of the bracts (Plate 4, fig. 7), each with two long lateral canals, was 

 likewise observed by Chun. 



In the two specimens in the series which are sexually mature all the gono- 

 phores are 9 , a fact suggesting that like " Amphicaryon", (Haeckel '88b, p. 193) 

 Mitrophyes may be dioecious; but the material studied is insufliicient to estab- 

 lish the point. The gonophores bear small swellings, or tentacular rudiments 

 on the bell margins opposite the terminations of the foin- radial canals, as in 

 various other Siphonophores. 



