630 SUilMARY OF CrKRENT RESEARCHES RELATING TO 



Prof. A. A. W. Hubrecht considers that in one group we do 

 find an organ ranking equal to tlie vertebrate notochord, and thus 

 supplying the much desired transitional form by which the Chordata 

 are allied to the lower Metazoa, and in fact to such forms as have 

 neither the much specialized organization of the segmental animals 

 (Arthropods and Annelid^) nor require to be turned upside down 

 before their homology with the lowest Vertebrate is admissible. The 

 proboscis of the Xemerteans, which arises as an invaginable structure 

 (entirely derived, both phylo- and ontogenetically, from the epiblast), 

 and which passes through a part of the cerebral ganglion, is homo- 

 logous with the ruilimeutary organ which is found in the whole series 

 of Vertebrates without exception — the hypophysis cerebri. The 

 proboscidean sheath of the Nemerteans is comparable in situation 

 (and development?) with the chorda dorsalis of Vertebrates. 



Hypophysis cerebri in Vertebrata and Tunicata* — Prof. W. A. 

 Herdinan states that in two specimens of Ascidia mammiUata which 

 he has lately had an ojiportunity of examining, the neural gland was 

 connected with the cloacal part of the peribranchial cavity only ; this 

 is just the position in which one would expect to find it, if the gland 

 had a renal function, and it appears possible that some arrangement 

 of this kind obtained in the primitive Chordata, previously to the 

 divergence of the Urochorda. " There may have been a renal gland 

 placed ventrally to the nervous system, not necessarily at the 

 anterior end only, and opening on the surface of the body by one or 

 more laterally-placed apertures, this gland being represented in the 

 Tunicata by the neural gland, and in the Vertebrata by the glandular 

 portion of the pituitary body." 



It is suggested that the connection of the so-called dorsal tubercle 

 with the neural gland is due to the enlargement of the pharynx into 

 a branchial sac, and the development of the peribranchial chamber. 

 It has been shown by Ussow and Julin that the dorsal tubercle is not 

 merely a sense-organ, while its complex structure indicates that it is 

 not merely the aperture of a duct. Further evidence must prove what 

 present evidence suggests, that it is a sense-organ into which the duct 

 of the gland has come to open. 



Origin of the Pellicular Cells.t — H. Fol has observed the process 

 of the endogenous formation of the cells of the ovarian follicle in the 

 ovum of Ascidians, and in some Vertebrates. The author's earlier 

 observations have been noted by various writers, and, of late, espe- 

 cially by Eoule and Sabatier. He now describes what he has seen in 

 Ciona intestinalis and Ascidia mammiUata; in the former the endo- 

 genous production commences by a thickening of part of the nuclear 

 envelope ; the nucleolus is generally found in the immediate neigh- 

 bourhood of this small diverticulum, and seems to give up a small 

 portion of its substance. The nucleolus is then carried to another 

 region of the nucleus, and the diverticulum becomes a solid bud, 

 which grows without losing its connection with the nuclear envelope ; 



♦ Nature, xxviii. (1883) pp. 284-6. 



t Comptes Eendus, xcvi. (1883) pp. 15Ctl-4. 



