Ixiv Journal ob' Comparative Neurology. 



The Development of the Vextrai. Ganglionic Chain of Insects. 

 The most important paper which has appeared for years on the ner- 

 vous system of arthropods is that of Veit CIrakek.I It is purely morph- 

 ological and embryological, lacking the histology in the strict sense, but 

 is well illustrated and afi'ords a number of new facts which we hope to 

 refer to in a fuller comparative notice hereafter. 



The Origin of the Nervous System in Polyzo.\. 



Davenport2 agrees with Hatschek's (as contrasted to Harmer's) 

 views that the brain is an invagination of the floor of the atrium. "The 

 nerve fibres are very evident in the adult ganglion of CristatcHa, and in 

 addition to them, there is a cavity, ontogenetically derived from the 

 atrium which contains no histological elements." 



The lophophoric nerves, passing down the middle of each lophophore 

 arm, are formed as outgrowths of the ganglion. The proximal part of 

 the lophophoric nerve is to be regarded as a pocket of the brain. "The 

 peripheral nervous system in rhylactohvmata arises from the brain as an 

 outgrowth of its walls." 



On the Innervation ol the Cerata of Some Nudibranchiata.3 



The cerata — dorso-lateral processes of the body wall — of the Nud- 

 branchs are innervated in various ways. In Polycera and Ancula they 

 are innervated entirely by the pleural ganglia ; in Dendronotus the pleural 

 ganglia are assisted by a few fibres from the pedal ; in Tergipes they are 

 innervated entirely by the pedal ganglia ; in Facelina the pedal ganglia 

 are assisted by a few fibres from the pleural. Ilerdmann thinks the evi- 

 dence at hand is sufficient to prove that in this case the nerve-supply can- 

 not be taken as a sure indication of homology. He also makes the fol- 

 lowing suggestion : 



" (i). These ceratal outgrowths may be truly epipodial, homologous 

 with the epipodia of Troc/ins, starting at first as pedal structures supplied 

 with nerves from the pedal ganglia; and (2) may have secondarily ac- 

 quired, possibly as the result of changes in form, position, and relations 



1. Studien am Keinistreif der Insocten, Denkschriften der Kais. Akad. der Wis- 

 senschaften zu Wieri., LVIL I'^'JO. 



2. BuL Mus. C(iini). Zool., XX, l. 



3. Herdmann, W. A. and J. A. Chvhi!. (Juart. .lour. Micro. Sci., Vol XXXIII, 

 pp. 541-558; pi. XXXII-XXXIV. 



