﻿3'|g CONTRIBUTIONS TO THE NATURAL HISTORY 



number, like the ambulacral tubes of which they are the continuation, and they converge 

 two and two, being more closely brought together in pairs towards the black speck of the 

 centre. (Plate V. Fig. 9.) In their respective position they differ somewhat ; though 

 rising from the four lateral ambulacra, they preserve a rather straight course from the 

 summit of the rows of fringes to the centre of the area ; the anterior and posterior ones, 

 however, bend towards the elongated part of the area, and follow obliquely the course 

 of its margin, thus contrasting in some degree with the lateral ones. How these tubes 

 terminate I have not been able to ascertain in a direct manner, but am inclined to 

 suppose that they empty into the lower bulbs of the funnel. The tubes are so fine, 

 and the circulation beyond the main stem of the chymiferous system is so easily stopped 

 as soon as the animal is not in the most favorable circumstances, and coarse materials 

 in addition to pure homogeneous liquids are so unlikely to be forced into these narrow 

 channels, as hardly to afford an opportunity to watch the direction of the current. 

 Perhaps a comparison of the different arrangements of these tubes in various genera 

 may lead to a more satisfactory result respecting this point of the circulation. 



I am equally at a loss to account for the precise connection between all parts which 

 may be seen around and above the central black speck (Plate V. Fig. 9 and 10). Even 

 the nature of this organ is very problematical. In its appearance it resembles somewhat 

 the marginal colored specks observed in Discoid Medusa?, and on that account has been 

 viewed by some as an eye-speck ; but by those who consider the so-called eye-specks of 

 Medusae as rudimentary auditory organs, it has been considered as an ear-speck. But 

 notwithstanding the difference of opinion upon its functions, all naturalists who have ex- 

 amined Beroid Medusa? have identified the black speck, which occurs in a central position 

 upon the extremity opposite the mouth, with similar specks occurring about the periphery 

 of Discoid Medusae. But in my opinion this comparison is not correct, and I am in- 

 clined to consider this organ or this speck as something similar to the central colored 

 speck which occurs in the middle of the disk in Discoid Medusa?, and which is particu- 

 larly distinct in young animals soon after they have been detached from the polyp-like 

 stem upon which they grew, — as a remnant of the connection which exists between the 

 mother stem and its progeny in those Medusa? which multiply by alternate generations. 

 This homology cannot for the present be sustained by direct observation, since the em- 

 bryology of Beroe is as yet entirely unknown. But I should not be at all surprised, 

 if Beroe were found to be the free Medusa form of some Hydroid Polyp from which 

 Medusa-buds have not yet been observed ; for the analogy between this central speck 

 and what might be called the remnant of an umbilical cord in Discoid Medusa? is far 

 greater than may at first sight be supposed. Its position in the centre of the summit 



