PLANTEO DE LA SITUACIÓN

to consider (86) later. The most common condition found in the oocyte nuclei of hypophysectomisod animals is illustrated in Fig8.ll, 18, and 13; recordings from corresponding control animals are given in Figs*14, 15, and 16* Although I have obsoryed a variety of changes in nuclear granularity following upon hypophysectomy, I have been able to distinguish two

universal characteristics of nuclei from animals which survived hypophysectomy for more than one month; euch nuclei ere either lacking in free granules, or they contain free granules greater than l#5p in diameter* Fig,17 shows the sises and general characteristics of the granules found in the nuclei of one

hypophyseotomised animal ; I have never seen objects like those in the nuclei of a stimulated animal. I have explored the possibility of tracing a sequence of changes in nuclear

granularity which maÿ take place during the first two weeks of hypophysectomy, but for the present purposes the task proved more exacting titan rewarding.

^.' *48*. O'- Df ’ Ghromosome. changes

(1) Gloat loops of ohromosomes 3(, XI, and XII,

There la one existing record of noa*homologown fusion between the giant loops of e&womoaomea XI and XII in eg m i f,ex mml there are two. similar records for T* e.kareliaii, The f&et thht these loops, can fuse with one another auggeata that thhir "matrices"* have certain properties in common, Assorted circumstantial evidence (see Callan & Lloyd 1960) points to the fact that the giant loops of chromosome X in camifex arc texturally similar to those of chremoaomea XI

w i i K Éim . w . i . i i i . I I « 11111. *111» gii * •

and XII# Thug we have in the giant loop# of c#rnife% three : conspicuous loci whose products are alike#

Because they are large and easily recognised, giant

loops offer excellent opportunities for the-study of physiological variability at specific'**gene loci". I have devoted some

attention to changés in the sisès of giant loops following hypophysectomy and gonadotrophin treatment# LOOp ai&e before

and after treatment was recorded photographically and/or by mûmnm of camera lucida drawings* photographs of complete chromosomes bearing giant loops were taken with the IPOM and a x 40 objective lens$ for drawings the system used was the same as that described on page 33 of this text, but for the present purposes the micro­ scope was fitted with a % 93 oil immersion objective and a % 10 eyepiece*

I- rujinuu.nr i i . r iirir^ jir m.Mn'irii i rr-i; rin.-r--TMTTfT;T"rT-^^i— r - — n i - '-"'-mi,f mY0r-,-wf,TrYTm f^iT r ni -i irfTrr-Tr-n r i "1 iY i-"r,rm r W m v n 'n ' ■ ' - r ‘ '■■' " ' ■*»■■■■* tMvfmmmtmtifm *

\y''\ ' '' "^/' \ / ' .. ' -" ' " - ." ' f t , ,\. ' \ ' *_

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lleeords of giant loop 6l%e were taken from twelve animals * four were hypophyseetomised, four treated with OG

(Bwias) and four treated with CG + PMS* Ae a rule the giant loops were recorded from three freehly-made preparations for each animal before and after treatment, but more extensive records were made for those animals whose giant loop» were at first unusually large*

Following the treatment of an animal^with gonadotrophin it» giant loop» may remain unchanged or may decrease in mime

according to whether they are small or large before treatment* Uhueimlly large giant loop», au,cli as those found in 36, 58, and 39 became m m H e r after treatment with gonadotrophin, (see Fig», 18 to 2i,')* Record» from control» 360 and 39C are given in

Figs,88 and 83. On the other hand I ImVe never Itnown gonado* trophin treatment to he followed by a marked increase in the »l»e of the giant loops. It 1» noteworthy that in 39, wiiich possessed giant loops on both homologue» of bivalent XII, there was at first a marked and consistent sine difference between the giant loops of one homologue and those of the other (Fig,20a)$ the difference was still apparent after CG + PW8 treatment, in spite of a general decrease in giànt loop siae (Fig.&Ob), In 32, 38, and 39 opposite member» of giant loop pairs were at first conaistontly fused on one homologue of chromosome XI but separate on the other homologue, (Fig8#19a, 81a, 86a, and 27a). After treatment this state of fusion was unchanged, (Figs,19b, 81b, 8Gb, and 87b).

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The effects of hypophyaectomy upon the giant loops were less obvious. In the majority of animala the siae of the giant loop© at the end of the experimental period did not differ significantly from their siae before hypophyseotomy. I have recorded a significant increase in giant loop aiae in

only one animal (13). Drawing# of the giant loops of chromosomes X and XI in 13 before and 82 days after hypophysectomy are

given in Flga; 84a and 24b, I have not explored the possibility that marked changes in giant loop sise occur during the first two weeks following hypophysoctomy, nor have I had the

opportunity of hypophysootomising an animal whose standard*

•S)

size oocytes possessed unusually large or small giant loops* such animals are comparatively rare,

ii) The spheres on chromosomes V and VIII,

The information which I shall offer concerning physiological variability at the sphere loci is mainly a synthesis of isolated observations. Certain well defined characteristics of spheres were repeatedly found in animals which had received a particular treatment* each characteristic can be associated with physiological activity or inactivity according to the nature of the treatment. In the early

stages of my work* however, it soemed that hypophysoctomised animals had smaller spheres and fewer free spheres per nucleus

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than animals which had been treated with gonadotrophin#. I tried to assess this difference by measuring the total volume of sphere material per oocyte nucleus in each animal before and after treatment. For a given experimental animal I recorded the total number of spheres, bo# free and attached, present in five lampbrush preparation# made from etandard-size oocytes. The number so obtained I divided by 5 to give the values listed in columns (ii) and (iii) of Table 5. Further­ more, using the inverted microscope, camera lucida, x 99 phase objective and x 10 eyepieces, I measured to the nearest , the diameters of all the spheres present in these five prep- arations. From diameter measurements, individual sphere volumes in were calculated and a value ivhich I have called the AVERAGE SPHERE VOLUME (columns iv and v. Table 9) was obtained for each animal. Bata of this sort were not obtained for control animals.

Ï have already mentioned the nodules which formed on the spheres of newt after that animal had been treated with CO

(Swiss), For purely intuitive reasons I attributed the formation of nodules to hyperactivity of the sphere loci. Following

treatment with GG + PMB, I have seen in the nuclei of two animals (99 and ^ ) , spheres which were either in the process of fusing with one another or of dividing (Fig, 89); the latter explanation seems the more reasonable. In 38

before treatmeat. rbhe splièra at 11 utsitB ©îï oae bomolORwe of_{‘ < ■*. I} Chromosome V wa# conelGtently migaing. After treatment with GG (Swies) there were epheree ot 2 and 11 unite on both homo­

logues of ohromoeome V, but.the ephere at 11 unite on one homologue was always email. In 99 one sphere at 2 unite on one homologue of chromosome V was missing in all preparation* both before and after treatment#

As described by Gâllan & Lloyd (1860), small Spheres are homogeneous; larger example* frequently contain vacuole*, whilst in extremely large spheres there may be vacuoles and a, single refractile body within each vacuole. All attached spheres and many of the free spheres in 19 out of 88 experi­ mental animals contained vacuole* and internal'refractHe bodies (ïlîlls) after these animals had received treatment with gonadotrophins; but the spheres of hypophysectomiaed animal* never contained vacuoles or IRBs*

With regard to sphere volume and the rate of production of material at the sphere loci, the result* listed in table 9, if treated as a single body of data suggest that gonadotrophin stimulation or hypophysectomy have no effect, However,. I

attached some significance to the values recorded for 32 and 13» The marked increase in the amount of sphdre material per oocyte nucleus following the treatment of 38 with GG (Swiss) must

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loci I the converse applies to It' is noteworthy that