536 Causes and Course of Organic Evolution 



and barnacles to their substratum has usually, and probably 

 rightly, been attributed to antennary secretions. But it seems 

 not unlikely, in view of Korschelt's statements (172, II: 215) 

 and of the remarkable flexure in the body of cirripedes, that 

 Darwin's assertion as to the part by means of which "the at- 

 tachment of the larva at first takes place, does not correspond 

 to the frontal extremity of the body, but to the most anterior 

 portion of the ventral surface," may point to a similar secretion 

 and fixation as already indicated for endoproctous polyzoans 

 (p. 516). In any case further search deserves to be made for 

 pedal cement glands, or their rudiments, in Crustacea. 



As to the excretory apparatus, suggested homologies can 

 alone be made, for our knowledge is still too incomplete for 

 definite statement. Beside the longitudinal canals with their 

 lateral branches that end in flame cells, several descriptions 

 and figures of Hudson-Gosse would suggest that some rotifers 

 develop an added system in the head region, just under the 

 trochal disk. These are of two kinds: first, "in Pterodina 

 the tubules ramify and spread into broad fan-shaped plexuses 

 of flat laminae, filling the wide triangular areas on each side 

 of the mastax"; second, the so-called gastric glands. "These 

 organs take the form of large reservoirs of delicate texture 

 and wrinkled surface, joined to the oesophagus by long ducts, 

 and affixed by threads to the lateral canals or to the lorica" 

 (169, II: 138). Whether either of the above two structures 

 may in any way be the forerunners of and homologous with 

 the green or antennal glands and the shell gland of Crustacea 

 remains to be decided. 



It is worthy of note that, as amongst the scaphopod mol- 

 luscs, a distinct heart and circulatory system seem to be un- 

 developed in several entomostracan as in rotiferan groups. 



Without entering here into the relation of the primitive 

 layers of the body to the alimentary canal, or into the struc- 

 ture of the reproductive organs, where interesting homologies 

 could be traced, it may suffice to say that we would consider 

 the Crustacea to have developed continuously and directly 

 from certain evolving lines of higher Rotifera already named. 

 Further that this progression has taken place through the 

 simpler entomostracans like the Ostracoda, Copepoda, etc., 

 which for eons of ages have been and still are largely of fresh- 

 water habits. By gradual multii)lication of body-segments, 

 the multisegmented bodies of the Phyllopoda were built up, 



