49 



lation of the blood in the usual signification of the expression; as the blood contained in 

 the perivisceral cavity always surrounds immediately the organs enclosed in the same and 

 thereby effects their alimentation. 



There is however an important system of organs, the anomalous position of winch 

 in the star-fishes necessitates a peculiar arrangement of the blood-system; and that is 

 the nervous system. While all the other vital organs have their place in the common peri- 

 visceral cavity (cceloma) the chief parts of the nervous system, the so-called ambulacral nerves, 

 are, as already indicated, situated quite superficially immediately under the thin skin which 

 lines the ventral furrows, and entirely separated from the perivisceral cavity by the inter- 

 jacent ambulacral skeleton. In order that the nervous system might be alimented in the same 

 manner as the other vital organs, it was therefore necessary that apart of the blood-fluid should 

 be conducted to it. This is effected by means of the before mentioned system of canal-like 

 sinus which is immediately bounded below by the central parts of the nervous system, and which 

 has formerly, and doubtless erroneously, been regarded as composed of real blood-vessels of 

 an arterial nature. How the blood-fluid from the perivisceral cavity is conducted into these 

 canals, and whether the so-called heart really plays any part herein, is not yet so com- 

 pletely clear to me that I can venture to express any decided opinion. I have as above 

 mentioned, not been able to indicate with certainty any direct communication between the 

 upper end of the „heart" and the perivisceral cavity; and although its lower end seems to 

 be in immediate contact with the circular sinus that lies inside of the bucal membrane. 

 I have yet not succeeded in ascertaining by direct investigation that there is any actual 

 communication in both cases. The question might probably be best decided by experi- 

 mental injection in large living star-fishes, for which unfortunately I have no opportunity at 

 present. That there really exists a communication between the said canals and the peri- 

 visceral cavity, I consider in any case as given; as the fluid contained in them corresponds 

 entirely to that which is found in the perivisceral cavity, and like it contains small cell-like 

 globules (blood cells) which are set in motion by an interior ciliary arrangement. Likewise 

 I consider it to be very probable that at the point of the arms there exists a direct con- 

 nexion between this latter and the canal-like blood-sinus which run along jthe ventral furrows. 



d. The respiration. 



No special organs of respiration are found in the Brisinga. I have sought in vain 

 in the dorsal skin for the so-called respiratory tentacles which in most other star-fishes are 

 so distinct and numerous. They are quite certainly wanting in the Brisinga. The respira- 

 tion may therefore reasonably be supposed to stand in connexion with the reception of 

 water into the interior of the body, which appears to take place continually. Of the parts 

 of the water-system, the ampollffi belonging to the water-feet project more or less from the 



