534 GENERATION. [c HAP. XXXVI. 



aperture of the efferent duct is found to be variously modified, according to 

 the different circumstances in which the animal lives, and the modification of 

 its general form. In some classes, the females are very few in number, and 

 often whole colonies are developed from one female. This is the case amongst 

 the bees, termites, and ants, in which the great majority of the individuals 

 are found to be neuters or workers. In the pupa of these last, the generative 

 organs may be distinguished, but they afterwards become atrophied. Now 

 it appears probable, that the development of the female organs is dependent 

 upon nourishment ; for it has been found, that the larvae which are to become 

 fertile females, or queen bees, have been supplied with a much more stimulat- 

 ing kind of food than that upon which the workers have been fed. 



The generative organs are double and symmetrical in insects, and several 

 accessory organs are found connected with the efferent duct. Of these, the 

 most remarkable is a receptacle connected with the vagina of the female, 

 designed to receive the seminal fluid of the male. This vesicle is termed the 

 receptaculum seminis, and in it the spermatic particles of the male may be 

 kept in a living condition for a very long period of time. The ova are im- 

 pregnated as they pass the orifice of the duct of the receptaculum seminis. 

 Besides this last, there is another organ connected with the lower part of the 

 female genital organs, designed to receive the penis of the male. This is 

 known as the bursa copulatrix, which, however, is not universally present. 

 Mucous glands pour their secretion into the vagina near its external orifice. 



The arrangement of the ovaries differs considerably in various classes. The 

 gland usually consists of ccecal tubes, which are four or five in number, and 

 open into the summit of the efferent duct ; while in some the tubes open 

 separately in the sides of the duct. The number of secreting tubes is very 

 variable in the different classes. 



The testicles consist of two or more (and often there are very many) simple 

 coecal tubes, the arrangement of which varies much, and which open into 

 the vas deferens of the corresponding side. The vasa deferentia are often 

 very long and much convoluted ; in some instances they are dilated below, 

 so as to form a sort of vesicula seminalis. 



The copulatory organs vary much in their disposition ; usually they consist 

 of hard, horny valvular appendages. In some species, suckers are developed, 

 upon the legs ; and other arrangements are found for the purpose of retaining 

 the female during the act. 



The imperfect or larval form of many insects when they leave the egg, has 

 already been alluded to under the heads of metamorphosis and metagenesis, 

 or alternation of generations. 



VERTEBRATA. 



In the vertebrata, with the highest and most perfect development of the 

 generative function, we shall find the progressive elevation characterized by 

 greater complexity of structure, more protracted dependence of offspring 

 on parent, and closer relations of the two sexes. 



Fishes. There are three types of structure in the generative organs of 

 fishes. First, in the Cyclostomatous Group and in the Eel, the ovary consists 

 of membranous folds depending from the spine, between the layers of which 

 the ova are, at the spawning season, developed. When mature, they escape 

 by the rupture of the membrane into the general peritoneal cavity, in which 



