1884.] 109 [Hyatt. 



will probably be accounted for by concentration of development 

 in the species lie investigated ; it seems evident, however, that the 

 blastopore and the two invaginations referred to above are not 

 necessarily coincident even in the different species of Peripatus. 

 The results attained by Dr. Van Wijhe (Zool. Anzeig., vol. vn, 

 1884, p. 683) principally from the examination of the embryos of 

 ducks are very important in this connection. He found that the 

 neural canal communicated with the exterior by means of two 

 pores, one at either end, and concludes that the neural canal was 

 an organ through which water circulated, and thus explains the 

 existence of ciliated cells in a part of this canal. Under the hin- 

 der "neuropore " lay the blastopore, and these two, fusing, pro- 

 duced the " blastoneuropore," which in turn closed after having 

 built the permanent anus. The fore " neuropore " lay between 

 the folds which form the primitive olfactory organ, and this he 

 considers as indicating that the water must have entered at this 

 pore and passed out posteriorly. Van Wijhe also quotes Hatsch- 

 eck (Zool. Anzeig., 1884, no. 177) to show that the passage of 

 water actually occurs through the ciliated furrow of the neural 

 canal in the embryo of Amphioxus. Van Wijhe's results thus 

 identify the olfactory pit, and not the stomodeum, as the prob- 

 able invagination or vestibule which was primitively connected 

 with the fore neuropore. One cannot read the researches of 

 Dohrn, Balfour, Owen and Scott upon the origin of the olfactory 

 invagination, hypophysis and stomodeum in Petromyzon (Balfour 

 Comp. Embryol., vol. vn ; Dohrn, especially Mittheil. Zool. Stat. 

 Neapel, vol. iv, p. 172 ; also Scott, Morph. Jahrb., vol. vn, p. 158) 

 without becoming aware that this result of Van Wijhe has in a 

 measure confirmed the theory of Dohrn. It antagonizes that part 

 of Dohrn's hypothesis which claims that the olfactory, hypophy- 

 sial and stomodeal invaginations were derived from primitive gill 

 slits which united to form central openings, and opposes to this 

 view the very simple fact, that the olfactory organ must have 

 been derived from a median tube. Dohrn seems on the other 

 hand to have been the first to suspect that the hypophysis was the 

 homologue of the oesophagus of some invertebrate ancestor of the 

 Vertebrata, and Owen independently concurred in this view of 

 its homology. This could only have occurred in a type in which 

 the transfer of the respiratory function from the neural canal to 



