1899] EPITOKOUS FORMS OF ANNELIDS 381 



Ctenodrilus an arrested representative of the Cirratulidae, such a con- 

 dition being in agreement with the parasitic life led by some in the 

 coelomic cavity of Holothurians and Synaptae. The gemmiparous con- 

 dition of Ctenodrilus is probably associated with its parasitism. 



They consider that schizogamy is derived from epigamy, as Ed. 

 Meyer, Kleinenberg, and Eisig do. On the other hand, Ed. Perrier 

 regards schizogamy as the primitive condition, interpreting, for instance, 

 Lfderonercis as a colony of two individuals, the metamorphosed region 

 presenting in an aborted condition what is more fully seen in the 

 primitive state in the schizogamous Sylliclians. They observe that an 

 annelid normally increases by new segments in front of the pygidium, 

 and they regard as a complication the appearance of a formative region 

 at any other point. In other words, schizogamy is distinguished from 

 epigamy by that addition only, and logically, therefore, the former is 

 derived from the latter. 



In some forms epigamy, or the epitokous condition {Hctcvocirrus and 

 Mystidcs), is very simple, viz. the addition of tufts of capillary bristles 

 in a certain number of feet — a primitive modification resulting from a 

 physiological condition, and rendering the animal more mobile when 

 discharging its reproductive elements. 



Greater complication is seen in Exogonc and Heteroncrcis, yet only 

 one region of the body is much modified. Even in Mystides, Hctero- 

 cirrus, and Dodecaceria (B), the anterior segments do not acquire the 

 pelagic bristles, which occur only in the region behind ; and this agrees 

 with the functions of the parts, the anterior directing the movements 

 of the succeeding propulsive region. 



In some forms, at sexual maturity, as in Notomastus lincatus, Eisig 

 has shown that the abdominal region, charged with the genital products, 

 separates from the thoracic for a pelagic life, yet no morphological 

 change has taken place. A similar condition occurs in Palolo riridis, 

 the edible annelid of the Samoans and Tongese. 



The authors suggest as a plausible hypothesis that the phenomena 

 of schizogenesis progressively follow schizogamy, by an accelerated 

 embryogeny ; as, for instance, in the Syllidians. The consequence of 

 this acceleration is to make the propagation of the species doubly sure, 

 and independent of ordinary sexual reproduction. 



The internal modifications of such forms at the epoch of sexual 

 maturity are the rapid absorption of the stored materials, e.g. the 

 eosinophile granulations, the atrophy of the walls of the digestive canal, 

 the diminution of the muscles of the body-wall and its granular ecto- 

 dermic layer, and the prominence of the segmental organs. 



They group the phenomena thus apparent into three divisions, 

 viz. : — 



1. Phenomena of histolysis without external raeta- 1 p , ^f ( [ CC ^ 



morphosis or scissiparitv • • • .1 D ? 0C 7 °H X 1 



1 J [rott/opnt/iaf/iius. 



