112 THE ALTERNATING GENERATIONS 



to perform that office. The generative organs are, indeed, 

 in perfect (female) individuals, divided as it were into 

 two parts of very distinct natures ; the ovarium for the 

 preparation of the germ and the production of the egg, 

 and the oviduct and uterus in which the ova are as it were 

 incubated, and the germ and embryo sufficiently 

 developed to allow of its being born. Now, it is actually 

 the case, that no true ovari/ has been discovered in the 

 "nursing" (ammen) generations ; on the contrary, the 

 germs, as soon as they are perceptible, are situated in 

 organs which must be regarded as oviducts and uteri, as 

 for instance, in the most perfect "nurses' we are 

 acquainted with, the Aphides. In the " nurses' of the 

 trematode larva, Cercaria echinata, I have remarked, 

 that the germs in their earliest condition, are collected 

 into an organ at the root of the tail, which may pro- 

 bably be regarded as a uterus, and that they appear to 

 distend this organ gradually to the size of the whole body. 

 The accurate anatomical researches of Prof. Eschricht on 

 the SaljJiB, also show in the most precise way, that the 

 associated brood of the Salpcs does not originate from ova, 

 but that, as germs which are arranged in a definite 

 manner between the walls of a hollow organ, it is con- 

 tained in what can in no case be an ovari/, and which the 

 author has termed a " germ- tube," {Keimrohre.) This 

 organ lies in a cavity which may probably be considered 

 very nearly a uterus, which is however, always as it were 

 a secondary receptacle for the germs ; but in the present 

 instance, it cannot be shown that they have occupied any 

 previous receptacle or place of formation.* 



Prom what we at present know, we may probably 



* Accurate researches witli respect to these organs of the " nurses" in all 

 the above-mentioned forms of animals, such as hare lately been made by 

 Professor Eschricht on the Salpes, would be of extreme interest for the 

 physiology of generation, and would be a task worthy of a competent anato- 

 mist. I cannot refrain from agaiu directiug attention to the remarkable 

 organ in the Trematoda, the secretion of wliich in the perfect animal is ex- 

 pelled from the body, but in the " nursing generation," on the contrary, 

 remains withiu it, as being an organ which probably subserves the function 

 of generation, and favours that of " nursing" m the first generation. 



