of Molhisks in Holothuriae. 105 



The molluskigerous organ, on the other hand, was observed to be 

 attached to the head in one instance, while in twenty other cases 

 it was attached to the intestinal vessel alone. "W hether it has 

 normally a cephalic attachment or not then, at any rate the in- 

 testinal attachment is by far the stronger. When the animal 

 breaks up, it appears that the head usually separates from the 

 portion containing the intestinal attachment of the molluski- 

 gerous sac, and hence there is an a-priori probability that the 

 molluskigerous sac will not be found with the genital organs. 



Even should the latter break off from their cephalic attach- 

 ment and become perfectly free, it is just as likely that they 

 should slip into, and be inclosed in, some other fragment, as in 

 that which contains the sac. 



Xo value therefore can be placed on negative evidence in this 

 matter ; and for anything that appears to the contrary, the mol- 

 luskigerous sac and the generative organs may always co-exist. 



There is further, evidence to show that the molluskigerous sac 

 does not, as Prof. Muller had supposed, replace the ordinary ge- 

 nerative organs. 



Speaking of the three sacs whose cephalic attachment was 

 observed (Annals, p. 30), he says (Archiv, p. 17) : — 



u The attachment of the three sacs was close together between 

 the calcareous ring and the cephalic disc near the point of inser- 

 tion of the vesicula Poliana. 



" Hereabouts usually, the main stem of the generative organs 

 lies, but in the present case no trace of it was to be found. Unable 

 to investigate the matter further in fresh preparations, I never- 

 theless thought it px-obable that the sacs opened here, partly be- 

 cause I had not at that time discovered the generative organs in 

 any Synapta provided with molluskigerous sacs ; partly because 

 in the last-mentioned case the three sacs were attached close 

 together at one and the same spot. Recently, however, grave 

 doubts have arisen in my mind as to the meaning of this con- 

 nexion, especially on account of the circumstance that the trunk 

 of the generative organ opens, not between the oral disc and the 

 calcareous ring, but close behind the calcareous ring. 



" The contracted condition of the specimens preserved in spi- 

 rit allowed of no further elucidation of this point. 



" The third smaller sac had already in the recent state been 

 detached for microscopic investigation ; the two other larger sacs 

 were yet attached, and could only be separated by repeated and 

 violent tearing of their point of insertion with needles; but I 

 could arrive at no conclusion as to the mode of their insertion 

 and the relations of their outer extremities. 



" The sacs are very fine towards their torn-off ends, gradually 

 diminishing to y^th of a line in diameter. Further investigations 



