( 61a ) 

 SUMMARY 



OF CURRENT RESEARCHES BELATINO TO 



ZOOLOGY AND BOTANY 



{principally Invertehrata and Cryptogamia), 



MICROSCOPY, &c., 



INCLUDING ORIGINAL COMMUNICATIONS FROM FELLOWS AND OTHERS.' 



ZOOLOGY. 



A. GENERAL, including Embryology and Histology 

 of the Vertebrata. 



Unity of the Process of Spermatogensis in Mammalia.f — M. 

 Laulaine recognizes two periods in the process of spermatogenesis ; 

 the first is one of proliferation (formation of spermatoblasts), the 

 second of dift'erentiation (evolution of s2)erraatoblasts) ; the former 

 has been observed to take place either endo- or exo-genetically. In 

 the horse and the pig spermatogenesis is similar to that in the rat, 

 but the author does not agree with iialbiaui in regarding the pheno- 

 menon as exogenetic in character ; indeed, the term exogenetic can 

 only be used if we ceased to ascribe to it the meaning of there being 

 proliferation by budding, and limit it to the intervention of the ramified 

 cells first described by Sertoli. In mammals with an exogenetic method 

 of spermatogenesis, the spermatoblasts are collected by the cells of 

 Sertoli, and go through all the phases of their development on the 

 surface of these cells ; the last are only permanent elements of sup- 

 port. In all mammals proliferation takes place by division. 



Formation of the Blastoderm in the Bird's Egg.t — M. M. Duval 

 denies that there is any absolute line of demarcation beyond the germ 

 proper and the white yolk ; indeed, we cannot even say that the 

 " vitellus de formation " only takes part in the process of segmentation, 

 and that the "vitellus de nutrition " has no share in it, for after the 

 formation of the blastoderm a secondary segmentation goes on in the re- 

 mainder of the yolk ; and it is impossible to say exactly where this 

 secondary segmentation ends. Segmentation, as Kolliker has pointed 

 out, is excentric, or commences at a point which does not correspond 



* The Society are not intended to be denoted by the editorial " we," and they 

 do not hold thenisdvefl responsible for the views of the authors of the papcM 

 not<d, or for any claim to novelty or otherwi.so mado by tliein. The object of 

 this part of tl:e Journal ia to prf;senta summnry of the pajiersa.? actually jn/bfis/ted, 

 and to describe and illustrate Instrurnents, Appanitus, &c., which are either new 

 or have not been previously described in this country. 



t Coraptfs Rendus, r. (1885) pp. 1407-9. 



X Ann. Rci. Nat.— Zool., xviii. (1881) 208 pp. and 5 pin. 



2 8 2 



