( 425 ) 

 SUMMAKY 



OF CUEEENT EESEAKCHES RELATING TO 



ZOOLOGY AND BOTANY 



{principally Invertehrata and Cryptogamia), 



MICROSCOPY, &c., 



INCLUDING ORIGINAL COJIMUNICATIONS FROM FELLOWS AND OTHERS." 



ZOOLOGY. 



A. GENEHAL, including Embryology and Histology 



of the Vertebrata. 



Development of Petromyzon (the Lamprey).! — Mr. W. B. Scott's 

 paper on this important subject is divided into five parts. In the first, 

 in which his own observations are not numerous, he deals with the 

 maturation of the ovum, and points out that if Calberla's results 

 are' correct, Petromyzon differs from all other vertebrates by the 

 following characters : — (1) No part of the germinal vesicle is extruded 

 from the egg, and the greater part passes into the ovarian nucleus ; 

 which (2) is uncommonly large, and consists of various parts ; (3) there 

 is a great difierence between the size of the nucleus of the ripe and of 

 the unripe egg ; (4) the germinal vesicle is said to become part of 

 the ovarian nucleus long before the egg is ripe. 



The second part deals with the cleavage period and the formation 

 of the germinal layers ; Schultze and Owsjannikow believed that 

 cleavage was complete, while Calberla foimd that the orifice of the 

 micropyle became converted into the first cleavage-groove, and that the 

 result of this division is the formation of two unequal spheres. As 

 usual, the smaller sphere and its products divide more rapidly than 

 the larger, round which in time they grow. Mr. Scott does not find 

 that two unequal spheres are constantly developed. The cleavage 

 cavity is at fijst noticeable on account of its great size ; it becomes 

 smaller during the invagination period, and appears to be covered by 

 a layer of cells, which do not belong to the ectoderm, but to the 

 mesoderm or the endoderm ; this is different to what obtains in most 

 holoblastic eggs. 



The gastrula is formed by a true invagination, which, however, is 



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

 authors of the papers referred to, nor for the manner in \shieh those views 

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

 summary of the papers as actually jjublished, so as to ])rovide 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 addicssed to the authors. 

 (The Society are not intended to be denoted by the editoiinl " we") 



t Morph. Jahrb., vii. (1881) pp. 101-73 (5 pis.).' 



