76 SCIENCE PROGRESS. 



conceptions of the inter-relationships of certain of the 

 great classes of animals with which he deals, by striking at 

 the most diagnostic of their morphological differences ; and 

 it may be well to briefly recapitulate some of the more 

 salient of its points, beyond what has been already said, be- 

 fore considering the two monographs specially under review. 



The discovery of the complex nature of the post-caval 

 vein, and of the existence in certain fishes of a post-caval 

 sinus, 22 together with the confirmation of Gunther's dis- 

 covery of a true vena cava inferior in the Dipnoi, 23 at once 

 cuts into the root of the ichthyopsidan stem ; and that of 

 salient points of morphological community between the oral 

 hypophysis of vertebrates and the ciliated sac of Amphioxus 

 and the Tunicates, 24 adds a link to the chain which binds 

 these animals together — -a link rendered the more secure (i.) 

 by appreciation of a parallelism of modification of the organ 

 in Amphioxus and the Marsipohanchii, as diverse from the 

 Tunicata and all higher vertebrates, 25 and (ii. ) by the discovery 

 in the Tunicate Oikopleura flabellum (?) of an abbreviated 

 condition of the endostvle akin to that of the Ammoccete. 26 



The importance until recently attached to the characters 

 of the occipital condyle is too familiar to need further 

 mention here, but the fact that in many birds and reptiles 

 the conditions are such that it might well be a nice point 

 in law to decide whether a single or double condyle is 

 present somewhat undermines this. The well-known fact 

 that, in Mammals more especially, the roots of the hypo- 

 glossus nerve arise recurrently with the ventral ones of the 

 spinal series and perforate the dura mater (and in many 

 cases the skull also) by distinct apertures, has become 

 luminous to an unexpected degree, by Froricp's brilliant 

 discovery 2T of their dorsal ganglionated roots in the embryo 

 ungulate. The investigations of Sagemahl, 28 Gegenbaur, 20 

 and others, which have followed this, and the discovery 

 of the persistence of dorsal hypoglossal roots in Protop- 

 terus 30 and Polypterus, 31 render it now tolerably clear that, 

 while in the Amphibia the hypoglossus nerve-bearing region 

 has gone over to the vertebral column, and in the Amniota 

 it has become merged into the occiput, in the Osteichthyes 



