Fecundation of the Ovum, 307 



the interior of the egg. Leuckart has even arrived at general 

 laws with regard to the structure of the micropyle in the different 

 orders. In the portion of this memoir which has now appeared, 

 only the Diptera, the Hemiptera and the Lepidoptera are re- 

 ferred to. The following is a summary of these laws : — 1. In all 

 the true Diptera (not including the Rhipiptera) the micropylian 

 apparatus consists of a simple opening, situated at the anterior 

 pole of the e^^j or at least in the neighbourhood of this pole. 

 2. In the Hemiptera the micropyles are almost always more 

 numerous, and not far from the anterior pole. 3. In the Lepi- 

 doptera the micropyles are always multiple, forming a variable 

 number (usually four or six) of canals, which rise from a common 

 central fossa situated at the anterior pole, and pierce through 

 the envelopes of the ^^^ in a radiating direction. As regards 

 the Crustacea, Meissner has ascertained the existence of the 

 micropyle in the Gammarus pulex of our brooks. 



It is curious that Bischoff, after placing himself in the ranks 

 of the defenders of the penetration of the spermatozoa into the 

 ovum, should have again taken up the pen* with a certain 

 degree of asperity to confute the discoveries of Meissner, which 

 appear to form the most brilliant point, and in a manner the 

 crown of their productions. Nevertheless, this does not in any 

 way invalidate the theory of the penetration of the spermatozoa 

 into the ovum, which is now permanently received into the 

 science. Bischoff in fact only questions the description given by 

 Meissner of the formation of the ova, and more especially of the 

 spermatozoa in Ascaris mystax. Meissner had regarded as 

 spermatozoa the same corpuscles which Nelson had previously 

 admitted as such, whilst Bischoff persists in regarding them 

 only as epithelial conules. On the other hand, Meissner, in 

 describing the formation of the ova by means of diverticula of 

 a germ-cell, had differed from Nelson, who had seen the young 

 ova totally destitute of vitelline membrane. Bischoff adopts 

 the opinion of Nelson, and positively denies the existence of the 

 germ-cells and their diverticula, at all events in the Ascaris of the 

 Cat. But he is greatly embarrassed by his epithelial conules 

 when it becomes necessary to find the true spermatozoa, which, 

 he says, must nevertheless penetrate into the egg. Notwith- 

 standing all this, Meissner, in a subsequent workf, remains 

 faithful to his theory. The future will decide this question, 

 which is only accessory here, seeing the abundance of other 

 materials. 



* Ueber Ei- und Samenbildung und Befruchtung bei Ascaris mystax, 

 Zeitschr. fiir wiss. Zool., Feb. 1855. 



t Beitrage zur Anatomic und Physiologie der Gordiaceen. Zeitschr. fiir 

 wiss. Zoologie, Mav 1865. 



20* 



