104 Prof. Midler on the Production 



naturally exist between a mere abstract of a paper and the paper 

 itself. It is very clear that the account read before the Academy 

 contained a full statement of all that its author then thought 

 upon the subject ; for, with the exception of one or two passages 

 which have been altered, the pi'esent essay is identical verbatim 

 et literatim with the former, differing merely in the presence of 

 very considerable interpolations at various places. The smaller 

 proportion of the added matter consists of new facts, the larger 

 of speculation somewhat cooled as it would seem by further con- 

 sideration. 



The principal new fact of importance (and its significance is 

 very great) is, that the molluskigerous sac has been found to- 

 gether with the ordinary generative organs in two cases. 



At page 5 of the ' Archiv ■ we find — 



" One of the first questions which arose was, whether the in- 

 dividuals with a molluskigerous sac also possess the ordinary 

 generative organs or not. The solution of this problem seems 

 easy enough, but was in truth very difficult, on account of the 

 violent rupture of the viscera by the spontaneous fission of the 

 animal — whence the genital sacs were not unfrequently torn 

 away from their attachment in the head. From this cause the 

 molluskigerous sacs were most frequently and readily found in 

 those portions of the body which had already become separated 

 from the head. In all those portions containing molluskigerous 

 sacs which I examined in Trieste, I sought in vain for the ordinary 

 genitals. On renewing my investigations here, however, upon a 

 large number of specimens preserved in spirits in which the head 

 was retained, I found two which possessed the ordinary gene- 

 rative organs as well as the molluskigerous sac. These genera- 

 tive organs indeed were not so large and completely developed 

 as they commonly are, but they contained quite normally-formed 

 ova of Synapta of 73-rd of a line in diameter. The collective 

 number of observations is by these increased to seventy-one : and 

 we must consider it as proved, that the presence of the molluski- 

 gerous sac docs not exclude the ordinary generative organs and 

 vice versa." 



Although the co-existence of the two organs has been abso- 

 lutely observed in two cases only out of seventy-one in which the 

 molluskigerous organ was found, a consideration of the nature 

 of the evidence will lead to the belief, that we must not thence 

 conclude that their co-existence is at all rare. 



The Synapta> were always found in fragments. The inclosure 

 of either generative organs or molluskigerous sac in any of these 

 fragments would depend either upon their being attached to 

 some portion of the fragment or upon mere chance. 



Now the generative organs are attached to the head only. 



