341 



XY.— A PKELIMINARY ACCOUNT 

 OF THE SPEEMATOGENESIS OF SPHENODON". 



By Lancelot T. Hogbkn, 



M.A.(Cantab.), D.Sc.(Lond.), F.Z.S., F.E.M.S., 



Lecturer and Huxley Curator, Imperial College of Science. 



{Read October 19, 1921.) 



Eighteen Tbxt-Pigubes. 



Seeing that the Tuatara is rapidly becoming extinct, the ojipor- 

 tunity of making some observations upon the chromosome com- 

 ponent of the germ cells merits record ; and it is the first duty 

 of the author to tender cordial thanks to Prof. Dendy, who 

 generously placed the material for the research at his disposal. 

 Hitherto no publications dealing with the cytology of Sphenodon 

 have appeared ; and our knowledge of gametogenesis among 

 Pteptilia as a whole is remarkably limited. The only data available 

 refer to two Chelonian and two Lacertilian genera. Jordan (1914) 

 issued a brief note on the first spermatocyte mitosis in Chrijsemis 

 and Cistudo, indicating the presence of an X-element in the 

 former. Trinci (1908) gave an admirable account of the synaptic 

 phenomena of Anguis, but was unable to furnish accurate data 

 respecting the diploid complex. Teilyesnicsky (1897) in an early 

 memoir on the histology of the testis quotes the number twenty- 

 four for dividing spermatogonia in Lacerta ; and Mile. Loyez in a 

 monograph on vitellogenesis mentions the same figure for the 

 oogonial chromosomes of Anguis and Lac&rta. There is thus no 

 complete study of gametogenesis in any reptile available at present. 

 Yet judging from the illustrations of Trinci and the phenomena 

 observed in Sphenodon the lleptilia should provide a most profitable 

 field of enquiry for those interested in chromosomal heteromorphism 

 and its bearing upon the theory of synapsis. 



The material here described consisted of a series of sections 

 7 to 10 mm. in thickness from the testis of a single individual 

 preserved by Prof. Dendy with aceto-bichromate ; though the 

 gonads were fixed in situ the microscopic detail proved on exami- 

 nation to be remarkably good ; and, while some of the more elusive 

 stages were not adequately treated, for most purposes the prepara- 

 tions were quite satisfactory. It would appear that the strength 

 of the reagent chanced to be approximately appropriate to the 

 osmotic pressure of the tissue fluids ; and owing no doubt to the 

 paucity of adipose tissue in any part of the organ penetration was 

 not unduly impeded in the outer layers upon which all the obser- 



