HETEROCHROMOSOMES IN THE GUINEA-PIG. 157 



In one very young animal only spermatogonia were fi.iiiid. Sertoli- 

 cells not having been differentiated, and n<> maturation stages 

 1 1 . i \ i n g yet appeare< 1 . 



The nuclei of the Sertoli-cell- ( Fig. i) are clearly different i 

 from those of the spermatogonia. They are larger and usually 

 flattened parallel with the wall of the tubule. In the rer. u T of 

 the nude' i large plasmosome and closely a--ocia!ed with 



it one, two or nn>re rhromatin nudeoli, or karvo-omes, which 

 otldi .tppiMi- to h.'' ntral vacuole. The retieulimi of the 



under u'n with thionin <>r iron-haematoxylin. 



Tin- 1 irg< r number of the -permaiovom'al nuclei eoiiiain ! 

 dump- of diroiu.uin of various and tangled thread- into 



which the clump lually resolved after a mitosis Fig. 2 . 



>hoi-i I mito-i- .ill nf the dump- disappear and a perfect 



spiren e i- formed 1 - In a young te-tis nearly aM 



"1 the nuclei are Minilar to I _ j. A fe\v are in -pircinc 01 

 |>rojih. i h ha- pn .\ ed .1 \ er\ dil'licnlt mal 



in dei ei mine the number of chromosomes either in the spermato- 

 ia orspermat [ have never found a case of a perfect !\ 



ilai plate \\here there was n-> overlapping. After spending 



it deal of tin me p"int. I ha\e concluded thai 50 



nd 7 is ;i:"l>abl\ llu t number. I i-. (> -!i..\\-. 



in outline the cliroiiio-oim-- of a ppipha-e. iv, ,m ,m aceto-carmine 



|ireparalion. the cell ha\in^ been much flattened. T\\o 1 

 pair- can be distinguished, and the oilier- vary con-iderably in 

 form and Fig. 7 i- the be-t equatorial pl.ite which \\.i- 



seen eiiher in .1 nniiie iu'eparalion- or in sections. I hi- 



\\.i- taken from Hermann mal. -rial Stained \\ith thionin. It will 

 ince be -een thai the chromo-oiiie- o\erlap in -udi a manner 

 a- l. maki' n curate < ountin;; difficult. T!ie one aberrant i hro- 

 nio-ome i- not a ch ristic feaiure. ( )ne unu-uall\ lonv pair 



of rod- i- conspicuous. There are -everal V's, and the remainder 

 ha\e the form of -trai-ht <u- -oineuhat cur\e<l rod-. The t \\ <> 

 Ion- roil- an- always noticeable in an anapha-e, lagging behind 

 the shorter < hromosomes. The V's are probably ihe same chro- 

 mosomes \\hich ha\e the -pind!. --liber- attached centrally and 

 pa-- to the pole- a- V's in the fir-t maturation mito-is. The 

 heterochromosomes one cannot distinguish at this stage with 



