364 CONTRIBUTIONS TO THE NATURAL HISTORY 



scribed area, and with the black speck in the centre. This black speck has also a 

 distinct ring, and it has seemed to me almost evident tha this ring extends, in the form 

 of narrow tubes, along the margin of the circumscribed area, and also that the eight 

 narrow tubes converging from the summit of the ambulacral combs empty into this ring ; 

 and as the ring itself is a fold from the prolongation of the funnel into the cavity ex- 

 tending forwards and backwards under the circumscribed area, it would follow that these 

 eight tubes communicate here with the central chymiferous cavity, as they communicate 

 from below through the tube around the mouth, an arrangement which would complete 

 the circulation, the main movement of which would seem to follow the ambulacra down- 

 wards, with a small eddy upwards towards the eye-speck, and with a main recurrent 

 stream along the digestive cavity. I should add, that the relative position of the eight 

 narrow tubes from the ambulacra, where converging towards the anal area, differs con- 

 siderably between the different pairs, the two anterior and the two posterior ones being 

 very near together, almost in the longitudinal axis ; and the two tubes of the two lateral 

 pairs being, on the contrary, as far apart from each other as they are from the anterior 

 pairs. So that there seems to be only six tubes meeting the central funnel, when in 

 reality the anterior and posterior are each double, 



I have not succeeded in making out a distinct nervous system connected in any way 

 with the central tubercle, though numerous fibres diverging in all directions may be seen 

 in connection with the upper part of the funnel. But it has always seemed to me that 

 they are rather muscular fibres than nervous threads, for they change their length, and 

 are by no means so symmetrically arranged as might be expected in a nervous system 

 in these animals, when we know its disposition in other types of the class. This region, 

 however, and the periphery of the mouth, are the places to look for it. But notwith- 

 standine: all efforts, I confess I have failed in the search. 



With regard to Pleurobrachia, I have already expressed my opinion respecting the 

 organic nature of the central black speck, which presents precisely the same appearance 

 in Bolina, and the same general relations with the surrounding parts right and left, for- 

 wards and backwards, and below. The bulb below seems to me really to be simply a 

 central projection of the chymiferous cavity, the ring around it something like the ring 

 of Sarsia around its centra! tubercle, and the eight narrow tubes diverging from the 

 summit homologous to the four vertical tubes of the Naked-eyed Medusae, the whole 

 differing only by the presence of apertures through which the refuse matters are dis- 

 charged from the chymiferous cavity. 



The extraordinary transparency of the gelatinous mass, and the impossibility of pre- 

 serving the animal after death in a contracted state, forbid the prospect of ever knowing 



