216 M. A. Baur on Synapta digitata 



Fig. 16. The same. Permian. Celluliferous face, worn; magnified 12 

 times. Tunstall Hill. 



Fig. 1 7- The same. Permian. Celluliferous face, unabraded ; magnified 

 12 times. Tunstall Hill. 



Fig. 15. The same (Fenestella plebeia, M'Coy). Carboniferous. Non-cellu- 

 liferous face ; magnified 6 times. Beith. 



Figs. 14, 18. The same. Carboniferous. Celluliferous face, worn; mag- 

 nified 12 times. Beith. 

 [Carboniferous specimens marked C ; Permian specimens marked P.] 



XXII. — On Synapta digitata and its supposed Parasite. 

 By A. Baur*. 



I. The attachment of the Molluskigerous Sac to the head of 

 the Synapta. 



The point the elucidation of which is of most importance 

 with regard to the relation of the sac-producing Mollusca to the 

 Holothurid is the case, once seen by J. M tiller, in which three 

 molluskigerous sacs were attached within the head of the Synapta. 

 J. Mtiller remained in doubt as to the meaning of this attach- 

 ment, the mode of adhesion, and the nature of the outer extremity 

 of the sac ; he considered further observations upon the con- 

 stancy or inconstancy of the attachment to the head to be 



necessaryf. 



Captures of Synapta digitata, continued during three months, 

 furnished me repeatedly with molluskigerous sacs thus attached. 

 It was also possible to examine more closely the mode of attach- 

 ment, and to settle by observation the question whether it was 

 constant or inconstant, whether it was accidental or connected 

 with the origin of the molluskigerous sac, or perhaps with the 

 immigration of the molluskigerous parasite. 



While among 100-200 individuals of Synapta digitata it is 

 not easy to find more than one infested by a molluskigerous sac, 

 or now and then by several, there were three out of 120-130 

 Synapta containing molluskigerous sacs, in which the sae, 

 besides being attached as usual to the intestinal vessel, at the 

 same time turned its ordinarily free and posteriorly directed end 

 towards the head of the Synapta, and was attached there like- 

 wise. In all the three cases the sac attached to the head was 

 of the same nature ; it differed, also, in no essential point from 

 the others, which in other individuals extended freely backward 

 into the body-cavity of the Synapta. None of the three mollus- 



* Translated by W. S. Dallas, F.L.S.,from the Monatsbericht der Akad. 

 der Wiss. zu Berlin, April 1862, p. 187- 



f J. Muller, " Ueber Synapta digitata und liber die Erzeugung von 

 Schnecken in Holothurien," p. 15. (See ' Annals,' February 1852, p. 106.) 



