44 HISTORY OF CRUSTACEA. CHAP. VI. 



division of the primary form into subordinate groups, 

 or because, at least at the time of this division, the 

 varying heart had not yet become fixed in any new 

 form. Where, on the contrary, respiration remained 

 with the anterior part of the body, whether in the 

 primitive fashion of Zoea, as in the Tanaides, or by the 

 development of branchiae on the thorax, as in the Am- 

 phipoda, the primitive form of the heart was inherited 

 unchanged, because any variations which might make 

 their appearance were rather injurious than advan- 

 tageous, and disappeared again immediately. 



I close this series of isolated examples with an obser- 

 vation which indeed only half belongs to the province 

 of the Crustacea to which these pages ought to be con- 

 fined, and which also has no further connexion with 

 the preceding circumstances than that of being an " in- 

 telligible and intelligence-bringing fact " only from the 

 point of view of Darwin's theory. To-day as I was 

 opening a specimen of Lepas anatifera in order to 

 compare the animal with the description in Darwin's 

 ' Monograph on the Subclass Cirripedia,' I found in the 

 shell of this Cirripede, a blood-red Annelide, with a 

 short, flat body, about half an inch long and two lines 

 in breadth, with twenty-five body-segments, and without 

 projecting setigerous tubercles or jointed cirri. The 

 small cephalic lobe bore four eyes and five tentacles ; each 

 body-segment had on each side at the margin a tuft 

 of simple setae directed obliquely upwards, and at some 

 distance from this, upon the ventral surface, a group of 

 thicker setae with a strongly uncinate bidentate apex. 



