With regard to the difference of the spermatic organs in males, if we are to investigate the causes of their existence, we must first grasp the final cause of the testes.Now if Nature makes everything either because it is necessary or because it is better so, this part also must be for one of these two reasons.But that it is not necessary for generation is plain; else had it been possessed by all creatures that generate, but as it is neither serpents have testes nor have fish; for they have been seen uniting and with their ducts full of milt.It remains then that it must be because it is somehow better so.Now it is true that the business of most animals is, you may say, nothing else than to produce young, as the business of a plant is to produce seed and fruit.But still as, in the case of nutriment, animals with straight intestines are more violent in their desire for food, so those which have not testes but only ducts, or which have them indeed but internally, are all quicker in accomplishing copulation.But those which are to be more temperate in the one case have not straight intestines, and in the other have their ducts twisted to prevent their desire being too violent and hasty.It is for this that the testes are contrived; for they make the movement of the spermatic secretion steadier, preserving the folding back of the passages in the vivipara, as horses and the like, and in man.(For details see the Enquiries about Animals.) For the testes are no part of the ducts but are only attached to them, as women fasten stones to the loom when weaving; if they are removed the ducts are drawn up internally, so that castrated animals are unable to generate; if they were not drawn up they would be able, and before now a bull mounting immediately after castration has caused conception in the cow because the ducts had not yet been drawn up.In birds and oviparous quadrupeds the testes receive the spermatic secretion, so that its expulsion is slower than in fishes.This is clear in the case of birds, for their testes are much enlarged at the time of copulation, and all those which pair at one season of the year have them so small when this is past that they are almost indiscernible, but during the season they are very large.When the testes are internal the act of copulation is quicker than when they are external, for even in the latter case the semen is not emitted before the testes are drawn up.
同类推荐
热门推荐
呆萌小甜心:冷少追捕999天
他,腹黑霸道的高冷总裁。她,看似精明常常犯迷糊的落魄千金。不是说他高冷吗?可为何总是纠缠她?“上官爵,奉劝你还是不要太投入的好,免得……”竹幼晴没在说下去。“免得什么?”上官爵来了兴致。竹幼晴挑了挑眉峰,眸光闪烁,大声道,“免得无法自拔!”“无法自拔?”上官爵悠悠的重复的了一遍她刚刚说的话。嘴角邪魅的笑容加深了些,垂首贴近了竹幼晴的耳边,“那……你帮我‘拔’不就好了吗?”男人特意加重了‘拔’字的发音。“……”樱桃班(阳光宝宝系列)
本书介绍了宝宝在6~9个月应锻炼爬的动作。爬行是宝宝运动发展过程中的一个重要阶段,是极好的全身运动,能锻炼肌力,为站立和行走作准备,还能促进宝宝手、眼、脚的协调运动,促进小脑的平衡。