THE BEGINNINGS OF LIFE. 533 



is, SO far as my experience goes, wholly unrepresented 

 in the development of the Rotifer — here the embryo 

 mass seems to shape itself more or less directly into 

 the future organism, and a similar direct process of 

 development without any antecedent stages of seg- 

 mentation seems to obtain amongst the Tardigrades 

 and the various forms of Mites. For although the 

 Tardigrades represent the lowest terms of the Articu- 

 lata, and therefore belong to a higher type — yet their 

 grade of development is very low. So far as their 

 mode of reproduction is concerned, they seem to be 

 very closely allied to the large Rotifera : for the most 

 part no distinct sexual forms exist, and only imperfect 

 females are met with containing a rudimentary ovary 

 (often without a distinct external duct), in which large 

 gemm^ or so-called 'eggs' are formed. In the case 

 of the Nematoids, however, embryos are produced from 

 the heterogenetic matrices, which, though sexless at 

 first, subsequently develop into what we are accustomed 

 to call 'males' and 'females' — the latter possessing a 

 double tubular ovary with a distinct external duct^ in 

 which a few large ova are generally to be seen 1. 



The fact, therefore, that animals with such distinct 

 and specific organs — and of different 'sexes' too — 



* The typical form of this ovary is represented in Fig. i a. There is 

 good reason for believing that in many of the Nematoids reproduction 

 takes place by means of mere gemmae, though in other cases bodies 

 similarly produced are fecundated, i.e. stimulated by contact with certain 

 elements secreted by the male. 



