( 343 ) 

 SUMMAEY 



OF OUEBENT EESEAECHES RELATING TO 



ZOOLOOY AND BOTANY 



^principally Invertehrata and Cryptogamia), 



MICROSCOPY, &c., 



INCLUDING ORIGINAL COIDIUNICATIONS FROM FELLOWS AND OTHERS * 



ZOOLOGY. 



A. GEXESAL, including Embryology and Histology 

 of the Vertebrata. 



Mesoblast of Vertebrata.f — 0. Hertwig discusses several im- 

 portant points. 



1. We have bad statements to tbe effect that the mesoblast bas a 

 paired, and others that it has an unpaired rudiment. These con- 

 flicting views are due to the fact that some authors regard the median 

 set of cells as belonging to the mesoblast, while others look upon it 

 as part of the endoblast ; against this latter it may be urged that the 

 set of cells in question cannot be separated off from the mesoblast, and 

 agaiast the former it may be said that there is no special peri-enteric 

 cell-layer lying below it. In connection with this we observe that 

 some authors regard the notochord as having a mesoblastic origin, 

 but 0. Hertwig believes that before long it will be generally allowed 

 that, so long as the notochord is not definitely differentiated, the 

 embryo, in the middle line, is still diploblastic. The dorsal median 

 set of cells should not be called either mesoblast or endoblast, but the 

 names of chorda-endoblast and enteric endoblast should be ascribed to 

 the two parts in this region. 



2. Taking next the vexed question of the origin of the mesoblast 

 from the endoblast or ectoblast, we find that an explanation is afforded 

 by the " ccelom-theory," for both endoblast and mesoblast arise by the 

 infolding of a membrane, which primitively bounded the surface of 

 the blastula. In Ampliioxus the gastrula-formation comes to an end 

 before the endoblast has become more complicated, and then it seems 

 as if the mesoblast arose from the endoblast. But in the higher 



* The Society are not to be considered responsible for the views of the 

 authors of the papers referred to, nor for the manner in -which those views 

 may be expressed, the main object of this part of the Journal being to present a 

 summary of the papers as actually published, so as to provide the Fellows with 

 a guide to the additions made from time to time to the Library. Objections and 

 corrections should therefore, for the most part, be addressed to the authors. 

 (The Society are not intended to be denoted by the editorial ' ' we.") 



t Jen. Zeitschr. f. Naturwiss., ix. (1882) pp. 247-328 (5 pis.). 



