290 THE GAMETOPHYTE, AND SEXUAL ORGANS [ch. 



perfect cell, viz. the ovum. The essential similarity of the archegonia of the 

 Bryophyta to those of the Pteridophyta, and the close analogies which 

 the antheridia and archegonia of the latter 

 show in their development and structure, 

 justify a similar conclusion for them also. 



The analogy of the sexual differentiation 

 of gametangia thus contemplated with that 

 of the differentiation of megasporangia and 

 microsporangia from a primitively homo- 

 sporous sporangium, so fully illustrated in the 

 Pteridophytes, cannot be mistaken. These 

 two progressions may be held to involve the 

 two most important evolutionary steps which 

 have followed upon the initial differentiation 

 of sex in the gametes themselves. Naturally 

 in Descent the differentiation of the game- 

 tangia must have preceded that in the 

 sporangia. For purposes of comparison the 

 microsporangium is regularly found to be 

 the more conservative in its characters, 

 continuing to represent the primitive state. 

 Thus it offers features of greater value for 

 comparison downwards: but the megaspo- 

 rangium is more prone to initiate new features 

 in accordance with the promotion of the 

 megaspore, consequently its special value is in Fig. 280. Bisexual archegonia oiMtiium 



T ■ T\ ^ o- -I 1 cuspidatit7n. j- = spermatocytes ; ?^c.r. 



comparisons upwards m Descent. Similarly = ventral-canal-cell; ^=ovum. (After 

 with the gametangia : the antheridium will Holferty.) (x 300.) 

 reflect more nearly the archaic type of gametangium, the archegonium being 

 a specialised advance upon it. Accordingly the former will present the 

 greater interest in relation to questions of phyletic origin, the latter will 

 be suggestive rather of later and derivative states. Prof, von Goebel has 

 suggested the propriety of establishing a conformable terminology for 

 both sporangia and gametangia. If the former are segregated by sexual 

 differentiation as mega-sporangia and micro-sporangia, so the latter may be 

 distinguished as mega-gametajigia and inicro-gametangia. 



It is not only in point of sexual differentiation that gametangia may be 

 compared with sporangia. The comparisons can also be drawn as regards 

 the relative size of the gametangia and sporangia in different types of plants, 

 and the Filicales offer good examples of this. Still it is necessary to remember 

 that these organs are essentially distinct in origin and in nature ; such simi- 

 larity as they show may be held as an indication of the general organisation 



