246 R. 1. PO(!()CK. 



alimentary canal and aorta is attested by the persistence of 

 the divisional line between its right and left hnlves. They 

 are merely united by a strip of connective tissue, perforated 

 above and below by the aortic and alimentary foramina^ 

 which must be regarded as the sole remnants of the open 

 space which originally separated the right and left portions 

 of the flap from one another. 



The neural ring in the Scorpions has its counterpart in 

 Actinopus, even to the development of an anterior median 

 process. It may have arisen in the same way by the fibrous 

 solidification and subsequent subneural fusion of the ventral 

 moiety of a pair of tergo-sternal muscles. If so, the view 

 that only one such pair of muscles is involved in its con- 

 struction, and that that pair belonged to the sixth somite of 

 the prosoma, is suggested by the absence of lateral perfora- 

 tions in the sides of the neural arch for the exit of nerves to 

 the appendages, and by the situation of the ring behind the 

 point whence the nerves to the appendages of the sixth pair 

 diverge. Equally well, however, may the sides of the canal 

 have arisen from the downward growth of the lateral portion 

 of the underside of the posterior portion of the entosternite. 



Lankester (6) suggests that the lateral process marked cr. 

 in the figure of the entosternite of Palamngeus (PI. 14, 

 fig. 20) corresponds to the antero-lateral processes of the 

 entosternite in Limulus. More likely, I think, is it that this 

 process is the thickened and solidified representative of the 

 posterior part of the crest developed (1*1. 14, i^gs. 21, 24) in 

 Centruroides and lurus, and finds its honiologue in the 

 similar crests in Thelyphonus, and not in the dorsal 

 apophyses, to which I believe the two processes in Limulus 

 are comparable. Nor can I agree with the opinion of 

 Schimkewitsch (10), that the lateral processes he finds 

 on the entosternite of the Scorpion named Androctonus 

 bicolor (see p. 231) are the homologues of the processes I 

 have numbered Itg., 2^/., and '^ty. in Thelyphonus. 



