302 



SEXUAL DIMORPHISM 



Here we come upon another phenomenon. It is we] 

 known that segmented worms, like many other animals, 

 have the power of producing again parts that have beei 

 removed naturally or artificially. This process is usually 

 called regeneration, but as the word generation is associate 

 with the idea of the production of new individuals or 

 spring, 1 prefer to call the process recrescence, which moi 

 exactly expresses its nature. Thus when the hinder part 

 a Syllis separates, the anterior portion may produce ne^ 

 posterior segments, and the separate hinder portion ma] 

 produce a head. The perfection with which the recrescence 

 of cephalic segments takes place in the sexual zooid after il 

 separation differs in different species, and the different forms 

 were originally, before their derivation from the asexuj 

 zooid was known, described as distinct species. 



In some species the sexual zooid produces eggs oi 

 spermatozoa (the sexes are distinct) without the recrescene 

 of a head at all. This is the acephalous zooid. 



In others no antennae or palps are produced, but a more 

 or less perfect cephalic segment is developed with one or two 

 pairs of eyes. Here we get the first indication of sexual 

 dimorphism in the sexual zooids. 



In others two rudimentary antennas or one pair are 

 developed in addition to the eyes. 



In others there are two pairs of antennas in addition to 

 the eyes. 



Finally, in others again the median antennas is added, sc 

 that there are five in all. These probably correspond to the 

 five appendages of the original asexual form, though they d< 

 not exactly resemble them, none of the five in the sexm 

 form being quite similar to the palps of the asexual. 



In the Autolytinse, separation of the hinder portion of the 

 body as a sexual zooid always occurs, but the process is 

 further complicated by the recrescence of new hinder segments 



