59 



resume in the limited space of this paper. Suffice it to say, lie shows 

 clearly the homological relations between the two orders in the struc- 

 tural affinities between the branchial sac of the Tunicata and the 

 palpi of the Polyzoa, in the relative position of the organs of nutri- 

 tion, the opening and termination of the intestinal tube, and in the 

 relative position of the nervous ganglion, and finally the correspond- 

 ing structure of their outer envelopes. He figures a Clavalina-like 

 Tunicate, and a Plumatella-like Polyzoon ; in his relative compar- 

 isons he has placed figures cf the two side by side in the natural 

 position in which they are found. The longitudinal diameter in both 

 is a line drawn from the base of attachment through the body and 

 parallel with the sides of the animal. To homologize the Lamelli- 

 branchiates with the Tunicates, we have only to compare the com- 

 mon Mya with an Ascidian, and the relation between the syphonal 

 tube of the one with the incurrent and excurrent orifices of the 

 other will be obvious at once ; and an anatomical investigation of the 

 two animals will render these relations still more apparent. Now, in 

 order to obtain the longitudinal diameter in the Brachiopoda, we must 

 follow the connection between typical forms of this order with mem- 

 bers of the order of Polyzoa ; look at the simplest Polyzoon where 

 the investing sac is a mere tube ; we have no appendage to the cell- 

 wall developed, though its bilaterality is plainly expressed in the 

 horse-shoe shaped lophophore ; but, as we advance, we find, on the 

 htemal side or region of the animal, as in Loricula and Eucratea, a 

 lid developed, called the operculum, which is strictly homologous with 

 the h^mal valve of the Brachiopoda. In the Lepralia and Flustra-like 

 foi'ms, this lid assumes more importance, and the homologies of the 

 retractor muscles of this lid with corresponding muscles in Tere- 

 bratula have been clearly pointed out by Huxley. If we lay one of 

 these Loricula-like forms in a normal position, do we not find that the 

 mouth, with the palpi, is at the free end of the body, as in Terebra- 

 tula, while the other end, that is, the neural portion of the cell, is 

 attached precisely as we find in Terebratula ? 



To make the case still more intelligible, let us compare the articu- 

 lation of the cell and operculum of a Cheilostomatous Polyzoon or 

 the two valves of an Avicularia with the two valves of the typical 

 Brachiopoda. The two valves in the latter case are articulated in the 

 same manner as obtains in the valves of a Polyzoon or in the valves 

 of an Avicularia. The shell of Brachiopoda consists of two valves, 

 — one large, through which the peduncle passes for attachment, the 

 other small, — which homologize with the larger and lesser valves 

 of Polyzoa. So, also, does the termination of the intestine turn 

 from the smaller valve in Terebratula as in the Polyzoon cited 

 above. Thus the brachial arms of the one are in strict homological 



