312 GENERAL SUMMARY TO 



between the full-grown Brachiopod and the Worm. The Brachiopoda constitute a large 

 and well characterised and distinct class or division among the Invertebrata, far too 

 important to be, as some have suggested, a simple division of Annelida. Their 

 position is lower than the Mollusca, and they form a well-distinguished order between 

 these last and the Annelida?. The setae do not appear to be a constant character, 

 and the tendinous peduncle of the Terebratulidae seems very different from the annu- 

 Iated structure which Morse describes in Lingula. It appears, according to Jeffreys, 

 to closely resemble the peduncle of a species of Anomia {A. patelliformis) ; Lingula 

 being moreover an aberrant form. Morse does not, however, fail to observe "in 

 considering the assemblage of remarkable characters in the Brachiopoda we must 

 recognise in them a truly ancient type. Thus while we do not find them in all their 

 characters resembling any group of Worms, I have endeavoured to show that all 

 their features, to a greater or lesser degree, are shared by one or other of the various 

 groups of Vermes, with one or two features of the Arthropods.'' Morse concludes his 

 elaborate series of observations by stating that we must regard the Brachiopods as ancient 

 cephalised Chatopods, while Serpula, Amp/ntrite, Sabella, Protula, and others, may be 

 regarded as modern (later) cephalised Chatopods. 



In the general summary of Kowalevsky's memoir by MM. Oehlert and Deniker, 

 1883, it is stated, " Let us now take up the other classes of Worms, and we shall find a 

 very great resemblance between the Brachiopods and the annulose worms (Chatopods). 

 The larvae of the Brachiopod have, as those of the Worm, three segments ; and, as with 

 these last, they have neither velum, nor foot, nor shell, and are segmented. 1 In the cephalic 

 or caudate segments that first appear, and between which afterwards appears the thoracic 

 segment, the only difference consists in that, with the Brachiopods the development 

 stops at this moment, whilst with the Worms new segments come to be added after the 

 intercalated segment. The bundles of bristles have arranged themselves in a similar 

 manner in the one as in the other larva ; they are present only in the thoracic segment, 

 and are wanting on the cephalic segment. It is only on account of a subsequent develop- 

 ment that these bristles find themselves carried back on the mantle of the Brachiopod : 

 at this period their disposition and their movements offer the greatest resemblance with 

 those of the bristles of Miiraria. The absence of bristles on Thecidium is explained by 

 the small development of the ventral side, which is due in its turn to the absence of 

 a peduncle. The existence of bristles during the larval period of the Brachiopoda has a 

 paramount importance ; they are not found in the Molluscs, nor Echinoderms, nor 

 even in other Worms besides the Chatopods, facts seeming to demonstrate, in an evident 

 manner, the relationship of these last with the Brachiopoda. The analogy is not limited 

 simply to exterior resemblances, but they exist also in the interior structure. Let us 



1 Brooks considers that the Brachiopoda are representatives of the highest specialised branch 

 of Polyzoa. The segmentation observable in Chiton, Pneumodermon, and Dentalium is absolutely 

 superficial. 



