CHANGES IN THE OVUM. m 



formed and developed without the direct intervention of the nervous 

 influence of the parent, as there is no communication between the nerves 

 of the uterus and the foetal envelopes ; and it has not been shown that 

 there are nerves either in the latter or yet in the umbilical cord. The 

 progressive animation of the new creature cannot, therefore, be derived 

 from immediate nervous propagation or direct extension of the nervous 

 activity from the mother to its offspring ; and we must look upon this 

 animation as originating in the embryo, and becoming developed under 

 the influence of inappreciable causes. At the very commencement of 

 embryonic life, the nervous system, which, in extra-uterine existence, 

 holds under its control the organic functions, appears now to have no 

 possible influence on the phenomena that gradually manifest themselves. 

 The primary changes in the ovum ocdur before the earliest traces of the 

 nervous system are apparent ; .and while its rudiments are forming, those 

 of other parts are also being developed. Even when the nervous system 

 has attained a somewhat considerable growth, it does not appear to have 

 assumed those controlling powers with which it is so largely endowed at 

 a subsequent period. 



In the homogeneous plasma of the ovum, in the common blastema, 

 coincidently or successively, a multitude of different parts are being 

 formed independently of each other, as if each contained within itself the 

 why and wherefore of its formation and ulterior perfecting. The nerv- 

 ous system itself seems to be submitted to the same general laws : it 

 does not appear to be dependent upon any other part, neither does any 

 part depend upon it ;.even when it is fully formed, the phenomena per- 

 taining to growth are evidently effected without its stimulating interven- 

 tion. Besides, it is well known that the monstrosities which are some- 

 times seen destitute of brain and spinal cord, may yet reach the end of 

 their fcetal development. True, certain facts have appeared to de- 

 monstrate that the formation of parts was dependent on nervous action. 

 In certain monstrosities, organs have not become developed when the 

 nerves which should have been distributed to them were absent; in 

 others, several organs have become fused together when their nerves 

 were similarly aggregated \ while an organ has been divided into frac- 

 tions corresponding to the accidental development of its nerve. The 

 muscles of the posterior part of the body of the foetus of the Cow and 

 Pig have been observed to be absent when the corresponding portion of 

 the spinal cord was, with its nerves, very imperfectly developed. But 

 these facts do not prove that the absence of the nerves was the cause of 

 the non-development of the muscles ; for in such cases there is a correla- 

 tion between the non-formation of the nerve and the absence of the 

 muscle ; the same cause which has hindered the formation of the one in a 

 certain part of the body has also prevented the growth of the other in 

 that part. And the same, to a certain point, with the relative develop- 

 ment of vessels and the increase of the parts to which they are distrib- 

 uted. In the original homogeneous plasma, there were developed the 

 diverse elements of an organ at the same time as its vessels, and the 

 force which created the connective, nervous, and muscular tissues, crea- 

 ted also the elements of the vessels — arteries, veins, and capillaries : 

 they are closely related to each other, and their growth goes on concur- 

 rently. If the vessels do not carry a sufficient supply of formative mate- 

 rial, the development of the part is tardy or ceases ; and, on the other 

 hand, if the latter from some cause becomes feeble and cannot assimilate 



