418 QUARTERLY CIlRONICLi; OF MICROSCOPICAL SCIENCE. 



no hint from the author as to whether the connection 

 in Lamellibranchs is really with the pedal ganglion or not, 

 nor does he touch on the case of the Cephalopods. One 

 thing is to be remarked about the auditory nerve. It is 

 a hollow tube, differing much in appearance from the other 

 nerves of the Gasteropods. It was this tube which Adolf 

 Schmidt thought formed a communication between the exterior 

 and the cavity of the otocyst. The reporter (E. R. Lankester) 

 is able to state definitely, from researches carried on at Naples 

 last winter, that the otolithic sac in Nudibranchs develops 

 from cells of the outer layer of the embryo, but never has any 

 communication with the exterior. In cephalopods, on the 

 contrary, he repeatedly observed its development by a pushing 

 in of the outer layer, the orifice of the cavity so formed 

 eventually closing in, and its neck remaining as the curious 

 little ciliated appendage of the otocyst described by KoUiker 

 in Loligo. 



Natural History of Dero obtusa. — In Professor Lacaze 

 Duthiers' admirable 'Archives de Zoologie Experimentale,' 

 M. Edmond Perrier commences an account of this interest- 

 ing Naidoid worm. In the part already published he de- 

 scribes the anatomy and structure of the annelid during its 

 period of scissiparity ; in a second paper he proposes to 

 deal with its sexually mature condition ; and in a third he 

 intends to describe the development. The respiratory appa- 

 ratus, with its four digit-like processes, situated at the anal 

 extremity, is well figured and described ; but it is from the 

 succeeding parts of M. Perrier's memoir that we expect to 

 derive the most information, since, with the exception of a 

 preliminary notice by Mr. Ray Lankester, in the 'Annals of 

 Nat. History,' 1870, no account of the generative organs of 

 a Nais has yet been published. 



The Layers of the Blastoderm in the Hen's Egg. — Professor 

 Peremeschko stated, at the meeting of Russian naturalists, 

 that though he, with Remak, recognised three layers, yet 

 he did not consider that the middle (mesoblast) developed 

 from the inner (hypoblast), but that it arose independently 

 from peculiar formative elements. These last, on account of 

 their deficiency in nucleus, belong to the category of cytods 

 (Haeckel), exhibit activemovements, and appear to take -their 

 origin from the white yolk. At the first they collect in 

 numbers on the floor of the segmentation cavity, and then 

 pass into the space between the outer and inner layers. The 

 three layers, therefore, arise independently of one another, 

 and can be readily separated, except at those spots where the 

 outer and middle layers become at an early period fused. 



