46 AMERICAN JOURNAL, 



aforesaid points in common, many other characters peculiar to 

 the individual classes are very diverse. In no point is this more 

 marked than in their embryology. The whole sub-type has been 

 removed from the mollusca by Moerch, while Prof. Morse, leav- 

 ing the ascidians (the most aberrant of all, and presenting more 

 than any other molluscoid group features which suggest affinities 

 with the Annulosa) Avith the mollusks, removes the Brachiopods 

 and Polyzoa and degrades to the rank of a subdivision of the 

 Annelids, two groups almost universally recognized as having 

 the value of classes. At the same time Dr. Moerch would annex 

 the Plathelminthce, Trematodes, Cestodes and Turbellarice, to 

 the Mollusca. Hoeckel, Gegenbaur and others, while leaving the 

 brachiopods with the mollusks, would carry to the Annulosa the 

 Polyzoa and Tunicata. While disagreeing with all these va- 

 rious efforts at dismembering the molluscan type, I cannot but 

 admit that, in the case of the Ascidians, at least, they are not 

 without some basis, though, as I suppose, an insufficient one, 

 but the classification which would leave these last with mollusks, 

 while depriving them of their companions the Polyzoa and 

 Brachiopods, would seem the most unphilosophical of all. 



Among the characters of this group which, from their incon- 

 stancy have little value, or are of value only in subordinate 

 groups, I may mention the fact that the circulating fluid (whether 

 due to the presence of haemoglobin or to other causes) differs in 

 color, being in the majority translucent, but varying from bluish 

 to red or even brownish in some forms, while others, closely 

 allied, have no such features. 



The majority of the Tunicates and Brachiopods, and all, or 

 nearly all, of the Polyzoa are fixed by an extension of the tegu- 

 mentary covering, which is usually of a horny texture, or by 

 the calcareous shell which is secreted by the mantle ; but this 

 character is not constant, even within the same genus, and a 

 great many brachiopods and tunicaries are entirely free. 



Transversely striated muscular fiber is found in many but 

 scattered instances, and, as a systematic character, cannot be 

 considered as of value. 



The modifications of the breathing organs are numerous, but 

 the apparatus as a whole preserves the same general relation to 

 the mouth — as regards its position. 



The vascular system is not thoroughly understood but exhibits 

 great diversities. 



The ovary is usually on the same side of the intestine as, and 

 near to, the heart, but this is not universal. In many forms 

 the ova undergo a sort of incubation before being expelled into 

 the surrounding medium. The Polyzoa and some Ascidians are 

 gemmiparous or propagate by buds as well as by eggs. 



