368 Dr. O. Hamann on the Phytogeny 



at least its terminal portion which rests upon the plate, can 

 very well be inflated by the water-vessel which terminates 

 cgecally in it, and in this way may be pushed forth, though 

 only to a limited extent. Perhaps Sea-urchins still exist in 

 which there are eye-spots like those of the Starfishes, and in 

 whicli the resemblance of the tentacles of the two groups will 

 be still greater. This, however, appears to be doubtful, 

 inasmuch as, where true organs of vision are at present known 

 in Sea-urchins, these have been found upon the surface of the 

 test, where, especially when present in great number, they 

 must be of essential service to the animals *. 



Of equal importance for the question of the derivation of 

 the Echinida from the Asterida is a comparison of their san- 

 guiferous spaces, i. e. the whole of the scMzoccele structures. 



In the Starfishes there is in the body-wall a system of 

 lacunae and hollow spaces, which have been in part described 

 as perihgemal spaces (Ludwig). All these lacunae and spaces 

 are gaps in the connective substance, schizocoele-spaces, as I 

 have demonstrated in opposition to the previous supposition 

 that they are parts of the enterocoele, by tracing their origin. 

 In the ventral wall such a schizocoele-space runs into each 

 arm. We find them again in the Sea-urchins in each ambu- 

 lacrum, and here likewise terminating cgecally, in this case by 

 the intergenital plate, in the former (Starfishes) by the ten- 

 tacle. But while in the Starfishes these five spaces or canals 

 unite in the centre to form an annular canal, which is con- 

 nected through the tubular canal with the schizocoele-spaces 

 in the dorsal body-wall, the conditions are different in the 

 Echinida, seeing that in them a masticatory apparatus has 

 been developed (probably from vertical plates) , and the tubu- 

 lar canal occurs only as a rudiment. Moreover, in the Sea- 

 urchins there is retained only a remnant of the schizocoele- 

 system of the dorsal wall of the Starfishes, in the form of the 

 schizocoelar anal ring, as I have already shown f, from which 

 structures lead to the sexual organs, like those presented by 

 the Starfishes. That all these phenomena may be easily 

 explained by the origination of the Sea-urchin from the Star- 

 fish is perfectly clear, while the reverse mode of origin seems 

 almost inconceivable, or, at any rate, is less probable. 



In the five schizocoele-spaces (longitudinal canals) of the 

 ventral wall (" perihcemal spaces " of Ludwig) of the Aste- 

 rida connective partitions (septa) have, as is well known, been 

 developed, and in these formation of unwalled spaces (the 

 blood-lacunse) has taken place. 



* See Sarasin's statements, Zool. Anz. 1885. 



t See also my " Vorlaufige Mittheilimgen," already quoted. 



