76 LECTURE VI. 



species, is scarcely less surprising. The ova are arranged in the 

 ovarian and uterine tubes like the flowers of the plantago, around a 

 central stem or rachis. There are fifty in each circle, that is to say, 

 you might count fifty ova in every transverse section of the tube. 

 Now the thickness of each ovum is 3^^^ of a line, so that in the length 

 of one line there are 500 wreaths of 50 eggs each, or 25,000 eggs ! 

 The length of each division or horn of the uterus is 16 feet or 2304 

 lines, which for the two horns gives a length of 4608 lines. The 

 eggs, however, gradually increase in size so as to attain the thickness 

 of -^Q of a line : we, therefore, have at the lower end of the horn 60 

 wreaths of ova, or 3000 ova in the extent of one line. The average 

 number through the whole of the extraordinary extent of the tube 

 may be taken at 14,000 ova in each line, which gives sixty-four 

 7nillions of ova in the mature female Ascaris lumbricoides ! 



The embryo is not developed within the body in this species ; the 

 ova may be discharged by millions, and most of them must, in large 

 cities, be carried into streams of water. An extremely small pro- 

 portion is ever likely to be again introduced into the alimentary 

 canal of that species of animal which can afford it an appropriate 

 habitat. The remainder of the germs doubtless serve as food to nu- 

 merous minute inhabitants of the water ; and the prolific Entozoa may 

 thus serve these little creatures in the same relation, as the fruitful 

 Cerealia in the vegetable kingdom stand to higher animals, and 

 minister less to the perpetuation of their own species than to the 

 sustenance of man. 



The oviparous Entozoa present, perhaps, the most favourable 

 subjects for studying with the requisite attention the successive steps 

 of that process by which the germinal vesicle and yolk become finally 

 transmuted into the young and active worm. 



I described and showed diagrams of some of these changes in the 

 ova of the Strongylus inflexus in my Lectures on Generation in 1 840. 

 Mr. Quekett* has since added other observations on the develop- 

 ment of the same species of Entozoon ; but the most accurate and 

 complete illustrations of the process had previously been published 

 by Professor Siebold f and Dr. Bagge:j:, from observations made 

 upon the ova of the Strongylus auricularis and the Ascaris acuminata, 

 both of them viviparous species of Nematoidea» Dr. Bagge finds at 

 the delicate blind extremities of the ovaria the germinal vesicles, which 

 are at first few and scattered, but become more closely aggregated as 

 they descend along the tube ; whilst the ovum is progressively 



* Trans, of the INIicroscop. Society, vol. i. p. 44. 

 f Burdach. Physiologie, vol. ii. p. 208. 

 X De Evolutione Strongyli, &c. 4to. 1841 



