IN THE ANIMAL KINGDOM. 69 



lying in the substance of the ovarian gland such at least 

 is the case in the higher animals ; but it is very doubtful if 

 these relations can be satisfactorily made out in all the lower 

 orders, though the ovum has very constantly the character 

 of a nucleated cell. It is commonly only the outer enve- 

 lope that dehisces, the ovum itself being merely penetrated 

 by the spermatic secretion, for the accomplishment of the 

 act of fecundation. It is not yet absolutely certain that 

 the spermatozoa always penetrate into the ovum in form ; 

 possibly in some cases there may be nothing more than a 

 transudation of their liquified substance. Their bodily 

 presence within the ovum, however, has now been so fre- 

 quently detected as to afford ground for believing a formal 

 penetration to be the usual rule.* We find, indeed, what 

 may be considered as a special provision for their intro- 

 duction, in the micropyle, which is found in many eggs, and 

 consists of one or more apertures at one of the extremities. 

 The functional import of the micropyle, as a passage of 

 access for the spermatozoa, is rather confirmed by the cir- 

 cumstance, that its homological relations are not the same 

 in all ova. In such as have been originally attached by a 



.* The first distinct observations of spermatozoa in the ovum appear to 

 be those of Dr. Martin Barry on the rabbit (Philos. Transact. 1840, 

 1841, 1843, March and June. Edin. Philosoph. Journal, Vol. LY., 326, 

 LVL, 36). They have also been observed by Dr. Farre in the earth- 

 worm, by Dr. Nelson and Meissner inAscwns (Philos. Transac. II., 1852), 

 and by Dr. Newport in the frog (Philosoph. Transactions, 1853, p. 266- 

 281). In the following year Bischoff, who had before discredited the 

 penetration of the spermatic particles, himself observed it, and since then 

 Siebold has detected it in the ova of the bee (True Parthenogenesis, p. 

 85), and Gengenbauer in those of Hydrozoa (Huxley, Oceanic Hydrozoa, 

 p. 22). Claims have also been advanced for Prevost and Dumas, Wagner 

 and Keber. Keber's statements have not received much consideration 

 from naturalists generally, except as regards the discovery of a micropyle 

 in the ova of Umo and Anodonta. A notice of the successive discoveries 

 in this department is given by M. Claparede Annals of Nat. Hist., 2d 

 Ser., Vol. XVII., 298. 



