258 CTENOPHOR.^. Part II. 



between the right and the left aml)nhicial tulie of the anterior and posterior pairs, 

 passing in their eonrse from the margin of the onter surface to the middle of 

 the inner surface, first descending, then rising, then descending again in nndidating 

 lines, then rising and descending again, until they meet to form an anastomose 

 in the lower central part of the lolje. Such a connection between any of the 

 tubes on the oral side of the body does not exist in Pleurobrachia. Besides the 

 meandering tubes of the long ambulacra, there may be seen, all over the inner 

 surface of the large lobes, a curious network of angular meshes, resembling small 

 vessels and connected with one another in a way which recalls somewhat the 

 branchial vessels of the Naiades, though tlieir arrangement is less regular and not so 

 strictly rectilinear and parallel. When I first noticed these meshes I mistook them 

 for real vessels, and have so described them in my paper on Beroid Medusa3 ; but 

 I have recently ascertained that they are simply the outlines of the gigantic po- 

 lygonal cells which form the inner layer of the large lobes. The ends of these cells 

 are flattened against the inner surface of the lobes and covered by small epithelial 

 cells, crowded in rows in the intervals or upon the outline of the large cells. A 

 similar network exists also in Leucothea formosa, Alcinoe rosea, and Bolina septentri- 

 onalis, judging from the drawings of Mertens. Will has dcscri):)ed the same thing 

 in Chiaja;^ but Milne-Edwards makes no allusion to it. Like Leuckart, Forbes, and 

 Milne-Edwards, I have seen nothing in Ctenophonx' answering to the so-called blood- 

 vessels described and figured by Will. 



The ambulacra of the sides are reduced to simple chj'miferous tuljes as soon 

 as they reach the base of the small loljes, whence the tulies continue in a very 

 complicated course through these lol)es, and then toward the mouth, sending also 

 a branch to the large k)bes. Each tulje first follows the inner margin of its small 

 lobe, then turns round the ol)tuse point of the lolje and retraces its course along 

 the outer margin of the same lobe to its very base ; here it branches in such 

 a way as to unite simultaneously with a tulje extending along the margin of the 

 mouth, and with the marginal tnl le of the inner snrfiice of the large lobes : or, it 

 may rather be said, an anastomosis is estaJjlished at the base of the small lobes, 

 on their external margin, with a recurrent tube {Fir/s. 88 and 89 ir) trending along 

 the outer margin of the large loljes, as well as with another tulje rising from the 

 margin of the mouth. Fir/, o of PI. ^"11. of my paper in the Memoirs of the 

 American Academy, in which the inner surface of the large loljes is turned outr 

 ward for the whole extent of their margin, shows these connections most distinctly.^ 



^ Will, Ilonv Trrgt'stiiW'. ji. 5."», PI. I. Fiij. - The letlcr-prcss mentions also distinetly these 



14, considers these meshes as forming part of the anastomoses, (p. 3.58). I am therefore surprised that 



skin, and describes them as similar in structm-r t<i Milne-Edwards should state that I have failed to 



the tentacular threads. notice the connection of the '' canaux costaux late- 



