404 



DISCOVERY REPORTS 



here and there. The nuclei of the cells lining the alveoli are larger than in the lactating 

 gland, and stain less densely. 



The thickness of the gland during this stage rarely exceeds lo cm. 



The resting stage occurs in a certain number of whales which are neither pregnant 

 nor lactating and has been found with one exception in the case of all pregnant whales 

 in which the gland has been histologically examined in this respect. It differs from the 

 intermediate stage principally in the size of the lobules (Fig. 138) which are definitely 







J^^^0}. 



■•'.'.V-O"' V ^•••' ■'•'•* ' " - " . . \ /. • " 





. i'r::^S:?-dy ^'l^'S^ " •/fri^—''':^;;'? •;•i■• 

 ?.VtTi' . ■ . ';'•'•;',■'■■■■ • r.;-?-.' ••.'•«■!/'•'•■•;••,• . 

 .-■;C"v<'^- • ::&■■■■■■ ■ .i^-^"' •■•■■.■•' ^ ••."•••.■ 





Fig. 137. Section of mammary gland not completely 

 returned to the normal condition. 



.•»f.=:•^/^i■v^vv?:^;,!:;? 



Fig. 138. Section of mammary gland after 

 complete involution. 



smaller and more numerous in a given area of section. The nuclei are usually more 

 numerous in a given space but are similar in individual appearance. The alveoli have 

 shrivelled to such an extent that they cannot now be distinguished. Usually the lobules 

 are flattened or elongated in cross-section, perhaps owing to collapse of the gland as 

 a whole. This is not an invariable rule, however, and the appearance of the lobules no 

 doubt depends to some extent on the plane in which the section was cut. 



The thickness of the resting gland is usually between about 4 and 8 cm. and is 

 only a little less than that of the intermediate gland. 



The fourth condition of the mammary glands, which is found in young whales 

 which in all probability have never been pregnant, or are pregnant for the first time, 

 difl^ers from the state of the gland in immature whales only in a slightly better develop- 

 ment of the lobules which are still less developed than in the resting gland. This 

 condition has been found in several whales with only one or two corpora lutea. 



The thickness of the gland here is of course intermediate between that of the resting 

 and that of the immature gland. The latter is usually about 2 cm. deep. 



