280 Mi;- W-fplark on the Chitopidi^, 



conducts to the stomach, which is an irregular subcylindrical 

 cavity about double the diameter of the pyloric extremity; it 

 traverses the body^ forming a sudden curvature like the doubling 

 of a horse-shoe, and returns across the body with the posterior 

 portion parallel to the anterior one, commencing at the pyloric 

 oi'ifice a very long intestine of five or six transverse or oblique 

 folds, supported by the liver, and disemboguing as rectum, at 

 the centre of the posterior extremity between the branchiae. 



For further particulars we refer to the description of the type, 

 as well as for the liver, ovary, and foot, all which present no 

 essential variation from the molluscan type, except the double 

 oviduct, if such be the case. 



The Chitons are best illustrated by the patelloid section of the 

 class, from which they are inseparable, but there is scarcely a 

 group of Mollusca to which they are not allied. The posterior 

 termination of the rectum is not without example ; it is essen- 

 tially the same in Fissurella, and more or less so in many of the 

 BuUidce. and Pleurobranchida. ]\I. Deshayes observes, that the 

 want of eyes and tentacula has been adduced as denoting affinity 

 with the Annelida ; but, as we have already obsei'ved, why not con^- 

 pare these deficiencies with the Conchifera, their immediate pre^ 

 decessors ? And as regards the Gasteropoda, the absence of eyes 

 and tentacula is not unusual : for instance, Bulla cylindracea has 

 not a trace of these organs ; the Veliitina otis of authors, Mr. 

 Gray's Otina, has no tentacula ; some of the Bullidce are without 

 eyes, and others without tentacula; there are examples of the 

 Natica without eyes, and in the Dentalia both eyes and tenta- 

 cula are absent. Dentalium, in my method, is placed in the van 

 of the Gasteropoda, and Chiton follows ; both are closely allied, 

 and, we think, appropriately succeed the Conchifera. 



I do not say that with the latter, the characters of alliance are 

 very decided ; still on examination there will be found analogies : 

 for instance, in Chiton and Dentalium the branchise are placed 

 symmetrically, though varying in particular position. In Chiton, 

 though not in Dentalium, the anus has the same posterior site 

 as in the Conchifera and in some of the patelloid forms. The 

 strict sexual order of hermaphroditism appears to obtain in both, 

 and throughout the Patelloida to the Pleurobranchidse and Bul- 

 lidse, in w'hich a more influential plan of reproduction commences. 

 These notes, in conjunction with the special typical ones, only call 

 for a very brief summary, and we think a calm review of all the 

 circumstances that are adduced will go far to convince zoologists 

 that there is not a locus standi for any one organ in Chiton con- 

 trary to molluscan essential characters ; — all are confirmatory of 

 the Chitonida belonging to that class, and the only return we 

 can make per contra is — nil. 



