A Prelimmar!/ Account of the Spermatogenesis of Sphenodon. 343 



Parasyuapsis and telosynapsis are used in an altogether different 

 sense by plant cytologists (cf. Farmer, Ann. of Bot., vol. 26). 

 For the events which occur between the last preraeiotic telophase 

 and the heterotype metaphase the system of de Winiwarter (1900) 

 is now generally employed • — viz. (1) leptotene stage, or leptouemci, 

 for the initial stages in which the nucleus is filled with fine 

 attenuated filaments, generally (a notable exception being Wilson's 

 Hemiptera) displaying a polarized or "bouquet" orientation. 

 Those who advocate parasyuapsis contend that the leptotene 

 threads are diploid in number and identify a succeeding zj/gotene 

 (Gregoire, 1907 = amiihitcne of Jannsens, 1905) phase, in which 

 they are seen to be assorted in laterally approximated pairs, con- 

 tracted from the nuclear membrane in very many cases. (2) pachy- 

 tene stage, or pachynema., in whicli the reduced number of thickened 

 and undivided filaments is present in the nucleus : when con- 

 traction (synizesis) occurs it attains its maximum at this stage. 



(3) diplotene stage (also called strcpsitene), in which the reduced 

 chromatin filaments display a well-marked longitudinal cleavage 



(4) diakinesis, in which the definitive heterotype chromosomes or 

 tetrads lie well separated upon tlie nuclear membrane, the term 

 tetrad being used descriptively whether the Ijivalents are quad- 

 rangular or not, and without any theoretical inq^lication as to 

 their constitution or mode of subsequent division. The reality of 

 synapsis is inferred from the existence of similar heteroraorphic 

 groups (diploid chromosomes) in different individuals of the same 

 species : in the interpretation of synapsis the difficulty of referring 

 the axes of fission in the reduction divisions to the plane of 

 cleavage in the diplotene filaments from which the tetrads are 

 derived is the centre of controversy. 



The testes of Sphenodon consist of masses of tubules made up 

 of spermatogonia, spermatocytes, spermatozoa and sustentacular 

 cells, arranged as in Mammals except that there is only a very 

 small amount of vascularized connective tissue in their interstices, 

 and no signs of interstitial epithelioid elements are recognizable. 

 The spermatogonia constitute the outermost layer ; and as is 

 frequently the case, contiguous cells on the whole show similar 

 stages in nuclear history, so that mitoses commonly occur in groups. 

 The prophase chromosomes exhibit the same type of behaviour 

 that I have described in Lilelhda, appearing first as attenuated 

 convoluted filaments which progressively become shorter and 

 stouter in anticipation of the cleavage which is not manifest until 

 metaphase : at no stage is there anything suggestive of a con- 

 tinuous spireme. An insufficient sequence of well-preserved cells 

 in telophase were observed to provide critical data ; but a few 

 figures clearly indicated vacuolization and well-marked polarity 

 in the disposition of the filaments. The polarity of the telophasic 

 units has been emphasized again and again by botanical cytologists, 



