Bibliographical Notice. 319 



Dr. Willey's speculations bring to a climax the extremely interesting 

 series of researches on the primary divisions of the chordate coelome 

 and their communications with the exterior which we owe to 

 various members of the Cambridge school. 



Treating of the central nervous system, the following conclusion 

 is reached : — " The medullary tube of the collar of Euteropneusta is 

 the homologue of the cerebral vesicle only of Amphio,vus and the 

 ascidian tadpole, and probably represents no more than the primary 

 fore-brain (thalamencephalon) of Craniota ; the roots of Ptycho- 

 derida) arc genetically related to the epiphysial complex of Craniota : 

 in the crucial nuchal region of the Enteropneusta are therefore to 

 be found not the actual but the nearest possible approximation to 

 the actual primordia of the hypophysis cerebri and of the epiphysis 

 cerebri of Craniota." The genital pleurae of Enteropneusta and 

 their fate are discussed at some length, but not fully, and the 

 conclusion that '•' the genital folds of Euteropneusta, the atrial folds 

 of Amphioxus, and the medullary folds of Vertebrata belong to the 

 system of pleural folds of the body-wall, and are ditferentiated from 

 a common primordium," is hinted at rather than demonstrated. 

 The medullary tube of Enteropneusts is in some cases formed by 

 the closing in of medullary folds, and the continuation of this 

 process backward would bring the posterior neuropore into 

 association with the blastopore (primitive anus) and form the 

 neurenteric canal. With regard to the notochord of Enteropneusts 

 there are some verj' interesting observations. This structure, Avhich 

 is a complex one, is considered to have been originally a portion 

 of the postoral gut, the anterior part representing the functional 

 oesopliagus of the Actinotrocha. The ventral caecum represents 

 that of the Actinotrocha of Phoronis ISahateri ; the lateral pouches 

 are the vestiges of a pair of postoral but pretruncal gill-slits, and 

 are represented in Actinotrocha by the " pleurochords " and in 

 Cephulodiscus by actual gill-slits. The notochord of Ctphnlodhcus 

 is related to the vermiform process of the notochord of Entero- 

 pneusta, The tongue bars of the gill-slits are organs of respiration, 

 developed on the assumption of the latter function by the slits. In 

 Am]iliio.vus they have already become ontogenetically secondary 

 structures, and in the Craniota they are transformed into the 

 thymus. The parabranchial ridges of the Enteropneusta are 

 homologous with the endostyle of Cephalochorda and Tunicata. It 

 Avill be easily understood from the above remai'ks that Dr. Willey 

 regards the Enteropneusta as not merely alhed to the Chordata but 

 *' much nearer the direct line of Chordate descent than has generally 

 been supposed." 



The last of the three articles in the volume is by Mr. A. E. 

 Shipley, on the Echiurids collected by Dr. Willey. Mr. Shipley's 

 })aper contains a short report on the five species of Echiurids in the 

 collection, none of which are new, and a valuable revision of the 

 group, including a key to the genus Tlialasscma and some remarks 

 on the distribution of the genera. L. A. B. 



