Dibliojniphical Notice. 319 



Dr. Willey's spocuhitions bring to ii climax llio pxtromely inlcrcstiiig 

 series of researehes on tlie primary diviaiuns of tlio chordate ccclomo 

 and thoir coninmnications with tlio exterior which we owe to 

 various incinbors of the Cambridge school. 



Treating of the central nervous system, the following conclusion 

 is readied : — " The medullary tube of the collar of Enteropneusta is 

 the homologuc of the cercibral vesicle only of Amjihio.rns and tho 

 aseidian tadpulo, and probably represents no more than the primary 

 fore-brain (thalam(Micephalon) of Craniota ; the roots of I'tycho- 

 derida; are 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 

 tho actual primordia of the hypoi)hysis cerebri and of the epiphysis 

 cerebri of Craniota." Tho genital pleurae of Enteropneusta and 

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

 conclusion that '• the genital folds of Entex'opneusta, the atrial folds 

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

 system of pleural folds of the body-wall, and are differentiated 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 very interesting observations. This structure, which 

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

 of the postoral gut, the anterior part representing the functional 

 oesophagus of the Actinotrocha. The ventral caecum represents 

 that of the Actinotrocha of PJioronis h>ahateri ; the lateral pouches 

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

 are represented in Actinotrocha by the " pleurochords " and in 

 CephulidiscuH by actual gill-slits. The notochord of Ciphahdiscits 

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

 j)neusta. The tongue bars of the gill-slits are organs of respiration, 

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

 Auqihiihius they have already become ontogenetically secondary 

 structures, and in the Craniota they are transformed into the 

 thymus, Tho parabranchial ridges of the Enteropneusta are 

 homologous with the endostyle of Cephalochorda and Tunicata. It 

 will be easily understood from the above remaiks that Dr. "Willey 

 regards the Enteropneusta as not merely allied 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, Willcy, Mr. Shijilev's 

 jiaper contains a short report on the live species of Echiurids in the 

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

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

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



