Chap. III. GENUS BOLINA. 267 



the current is alway.s to and fro, from the main cavity to the tentacular bulb 

 and back. These tubes do not anastomose with the tentacular tubes. 



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 abactinal part of the funnel. But it has 

 always seemed to me that they were contractile fibres, or rather the fibre-like 

 angles of the motory cells, and not nervous threads, for they change their length, 

 and are by no means so symmetrically arranged as might be expected in the 

 nervous system of radiated animals, the disposition of which is known in some 

 of their types. This point, however, and the periphery of the mouth, are the 

 regions to which to look for it ; but, notwithstanding all my efforts, I confess I 

 have failed in the search, and only noticed the walls of motory cells. I have 

 already expressed my opinion respecting the nature of the central black speck of 

 Pleurobrachia. Tliis organ presents precisely the same appearance in Bolina, and 

 the same general relations with the surrounding parts. 



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

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

 knowing fully the arrangement of the contractile fibres throughout the body, unless 

 we obtain great improvements in the construction of the microscope, enabling us 

 to examine bulky animals alive, and to bury the focus to any depth of the sub- 

 stance of their body without removing the superficial parts. As far as I have 

 been able to trace the structure of the spherosome of Bolina, the general arrange- 

 ment of its cells is to a great extent similar to that of Pleurobrachia. The radi- 

 ating system of motory cells is nnquestionably the most extensive, though the 

 interambulacral system is the most conspicuous. Parts of the walls of its cells are 

 easily seen as bunches of fibres converging toward the intervals of the successive 

 combs of locomotive flappers, and extending brush-like across the interambulacral 

 spaces, though diverging in each bundle. These fibres seem more powerful, and, 

 at all events, far more distinct, than the vertical fibres, which I have never been 

 able to trace in continuous rows. 



Though I first obtained specimens of this species at short intervals through six 

 successive months, from December to June, I never succeeded in discovering the 

 sexual system, not even in the most rudimentary state, until I had an opportunity 

 of watching them uninterruptedly in the latter part of the summer and during 

 the autumn, when I found the ovaries and spermaries following the course of the 

 ambulacral tubes, as first noticed by Will, in Eucharis, and alternating with one another 

 in the eight interambulacra. The circumstance of my failing to trace the repro- 

 ductive system for so long a time, may show how great difficulties these investigations 

 are attended with, and how much remains to be done before the whole history 



