1891.] Mr Groom, On the Orientation of Sacculina. 163 



the organs compared in Lepas and Sacculina speaks very strongly 

 in favour of their homology in the two, and if this be the case 

 there can be little doubt as to the true orientation of Sacculina, 

 and that though the supposed development on which Kossmann 

 partly based his case has been shewn by Delage not to take place 

 it will be necessary to return to the older view based upon less 

 complete information, that the mesentery is dorsal and the 

 mantle-opening posterior. 



There is one more point to which I wish to draw attention. 

 The great similarity in structure and relation of the oviduct in 

 Lepads and in Sacculina makes it exceedingly probable that these 

 organs are truly homologous. Now in all Cirripedes in which 

 the position of the genital pores has been accurately determined 

 they are very constantly situated at the base of the first of the 

 six pairs of cirri 1 . In all probability then the portion of the 

 body on which the two oviducts open is thoracic. This conclusion 

 agrees well with the position of the ganglion which corresponds 

 closely with that of the largest ganglion of the Thoracica. I 

 would suggest then that when fixation of the Cypris-form takes 

 place a great reduction in size of the thorax occurs at the same 

 time as the moult accompanying that fixation, and that the whole 

 of the thorax and abdomen is not cast off in the way Delage 

 supposes, but that a portion, small perhaps, but morphologically 

 representing them is left attached to the head. This would indicate 

 a conception of the Rhizocephala differing considerably from that 

 proposed by Delage who considers the adult Sacculina to represent 

 the head alone of other Crustacea. The visceral portion of the 

 parasite would consist of head and thorax fused together; the 

 latter, judging from the position of the female genital pores, 

 occupying as much as one-quarter of the whole. The carapace 

 attached to the dorsal side of the head in Lepas and in the Cypris 

 stage of Sacculina must then be regarded as fused to the dorsal 

 side of the thorax as well as the head, in a manner analogous to 

 that of the higher Crustacea. 



(4) Some experiments on blood-clotting. By Albert S. Grun- 

 BAUM, Gonville and Caius College. 



[Abstract; received March 3, 1891.] 



In the ' Centralblatjb fur Physiologie' of 1888, p. 263, there is 

 a paper by K. Bohr on the respiratory changes due to injection of 

 peptone and leech-extract, and in this paper he incidentally 



1 I have lately been able to supply the only missing link in the chain of 

 evidence which points to Darwin's "Acoustic sacs" as marking the termination of 

 the oviduct : the eggs in one specimen of Lepas were found actually issuing from 

 the orifice of the sac. 



VOL. VII. PT. IV. 14 



