Book I chapter 11

At least they certainly produce their eggs in a soft envelope, the reason being that they have but little heat and so their nature does not complete the process of drying the egg-shell. Because, then, they are cold they produce soft-shelled eggs, and because the eggs are soft they do not produce them externally; for that would have caused their destruction.

The process is for the most part the same as in birds, for the egg descends¹ and the young is hatched from it near the vagina, where the young is produced in those animals which are viviparous from the beginning. Therefore in such animals the uterus is dissimilar to that of both the vivipara and ovipara, because they participate in both classes; for it is at once near the hypozoma and also stretching along downwards² in all the cartilaginous fishes. But the facts about this and the other kinds of uterus must be gathered from inspection³ of the drawings of dissections and from the Enquiries. Thus, because they are oviparous, laying perfect eggs, they have the uterus placed high, but, as being viviparous, low, participating in both classes.

Animals that are viviparous from the beginning all have it low, Nature here having no other business to interfere⁴ with her, and their production having no double character. Besides this, it is impossible for animals to be produced alive near the hypozoma, for the foetus must needs be heavy and move, and that region in the mother is vital and would not be able to bear the weight and the movement. Thirdly, parturition⁵ would be difficult because of the length of the passage to be traversed; even as it is there is difficulty with women if they draw up the uterus in parturition by yawning or anything of the kind, and even when empty it causes a feeling of suffocation⁶ if moved upwards⁷. For if a uterus is to hold a living animal it must be stronger than in ovipara, and therefore in all the vivipara it is fleshy, whereas when the uterus is near the hypozoma it is membranous⁸. And this is clear also in the case of the animals which produce young by the mixed method, for their eggs are high up and sideways, but the living young are produced in the lower part of the uterus.

So much for the reason why differences are found in the uterus of various animals, and generally why it is low in some and high in others near the hypozoma.

1 descends   

v.下来( descend的第三人称单数 )；下去；下降；下斜

参考例句：

• This festival descends from a religious rite. 这个节日起源于宗教仪式。 来自《简明英汉词典》
• The path descends steeply to the village. 小路陡直而下直到村子。 来自《简明英汉词典》

2 downwards   

adj./adv.向下的（地），下行的（地）

参考例句：

• He lay face downwards on his bed.他脸向下伏在床上。
• As the river flows downwards,it widens.这条河愈到下游愈宽。

3 inspection   

n.检查，审查，检阅

参考例句：

• On random inspection the meat was found to be bad.经抽查，发现肉变质了。
• The soldiers lined up for their daily inspection by their officers.士兵们列队接受军官的日常检阅。

4 interfere   

v.(in)干涉，干预；(with)妨碍，打扰

参考例句：

• If we interfere, it may do more harm than good.如果我们干预的话，可能弊多利少。
• When others interfere in the affair,it always makes troubles. 别人一卷入这一事件，棘手的事情就来了。

5 parturition   

n.生产，分娩

参考例句：

• Did the parturition go well yesterday evening?昨天晚上分娩顺利吗？
• She is a well-known parturition hastening midwife.她是这一带有名的催生婆。

6 suffocation   

n.窒息

参考例句：

• The greatest dangers of pyroclastic avalanches are probably heat and suffocation. 火成碎屑崩落的最大危害可能是炽热和窒息作用。 来自辞典例句
• The room was hot to suffocation. 房间热得闷人。 来自辞典例句

7 upwards   

adv.向上，在更高处...以上

参考例句：

• The trend of prices is still upwards.物价的趋向是仍在上涨。
• The smoke rose straight upwards.烟一直向上升。

8 membranous   

adj.膜的，膜状的

参考例句：

• Others are born live, after struggling to break free from a membranous egg sac. 其余的是冲破膜状蛋囊而出生的。 来自电影对白
• Thellos thellon, membranous layer of life is our only home. 薄薄的膜层就是咱们独一的家园。 来自互联网