386 R. T. GUNTHER. 



ducts of Chiton may only be the analogues of the oviducts 

 of Sagitta. 



The resemblance to certain Cephalopoda is also surpris- 

 ingly close. The body-cavity of the Cha3tognatha is in the 

 jnore primitive condition^ in that it remains divided longi- 

 tudinally throughout life, but owing to the fact that the 

 Cephalopoda are dioecious, there is not the same need for a 

 separation of the male and female gonads by a genital 

 septum that there apparently is among Chaetognatha. The 

 nervous system of Nautilus and Cha3tognatha are both modi- 

 fications of the same plan. Endocephalic skeletons, germ- 

 cells mounted on stalks, and last, but not least, the bilateral 

 " foot," hood-like and surrounding the mouth, are common to 

 both Nautilus and Chfetognatha. 



Another very remarkable fact is that the peculiar charac- 

 teristics of the Leioglossal Octopods — no radula, arms united 

 by a membrane, fins developed on the sides of the body — 

 are all characteristics of Sagitta. 



Although a few naturalists have already suggested that 

 the nervous system of the Mollusca and the Cha3tognatha 

 may indicate relationship, no one has hitherto pointed out 

 how perfect is the resemblance between the other organs of 

 the two groups. 



We have in the Chastognatha the key to many Molluscan 

 mysteries, not the least important of which is the develop- 

 ment of the Cephalopoda, which, owing to the presence of a 

 large mass of inert food-yolk, has been profoundly modified. 

 In fact, in the matter of developmental history, Sagitta 

 would seem to bear the same relationship to the Cephalopoda 

 that Amphioxus bears to the higher Vertebrata. 



If our theory be correct the Chaitognath type of develop- 

 ment may be that of the Pre-Siluriau ancestors of Nautilus, 

 and probably of the earlier straight-bodied Cephalopoda, 

 such as the Orthoceratida) and the Bactritidee. 



A further inference of far-reaching importance is that 

 the crawling Archimollusc of Lankoster was not the common 

 ancestor of the entire Molluscan phylum, but only of the 



