18 THOS. h. MONTGOMERY, 



unipolar, though froni the one fibre pole a number of fibres may 

 proceed; and in such evidently unipolar cells it is characteristic for 

 the nucleus, that its chromatin is massed together in that portion of 

 the nucleus, which lies nearest the fibre pole ; thus the chromatin mass 

 frequently assumes the shape of a concavo-convex lens (Fig. 18). The 

 mesenchym cells of the caudicle, bear a close resemblance to the 

 embryonal mesenchym cells of Malacohdella, described by v. Kennel 

 (77). 



Some weeks after I had determined these unique relations, of 

 the mesenchym elements in the caudicle of Cerebratulus lacteus, and 

 had sent to the "Zoologischer Anzeiger" a preliminary note, announcing 

 these results among other items, I had my first opportunity to com- 

 pare Burger's recent Monograph ('95 b). In this work the author 

 states (p. 238): "Die Haut und besonders die Muskelschichten und 

 das Parenchym (sie!) des Schwänzchens zeichnen sich vor denen des 

 Körpers durch ihren auffallend grossen Reichthum an Kernen aus und 

 machen somit den Eindruck embryonalen Gewebes. . . . Die gallertige 

 Substanz des Parenchyms ist sehr wenig, dagegen sind die Parenchym- 

 zellen sehr reichlich entwickelt." With the exception of Bürger and 

 myself, no investigators have noticed these interesting histological 

 points. 



3) Parenchym tissue (Figs. 19, 21 Par). This forms a 

 single layer around the dorsal and lateral blood vessels, and their 

 commissures, and a layer around the proboscis sheath, except where 

 the latter is dorsally in contact with the inner longitudinal muscle 

 layer; parenchym cells come into contact with the intestine, only 

 where the blood vessels approach the latter. This tissue is absent 

 in the caudicle. The cells have the same histological structure as in 

 Carinella. In comparing the occurrence of these cells in the last- 

 named genus, with their occurrence in Cerebratulus^ we find that in 

 the former they are most abundant in the anterior trunk region, 

 whereas in the latter genus they become more numerous posteriorly. 



CoE ('95) has briefly described these cells in C. lacteus, and 

 Bürger ('90, 95 b) more minutely for other species. The latter in- 

 vestigator states ('90, p. 89) : "Wir werden sofort sehen, dass die Um- 

 wallung der Gefässrohre von Parenchymzellen nur dort statt hat, wo 

 jene frei im Parenchym des Leibesraumes und nicht von Körper- 

 musculatur, wie in der Kojjfspitze, eingeschlossen liegen. So muss es 

 uns wundern, dass das Rückengefäss auch dort den Mantel der 

 Parenchymzellen nicht verliert, wo dasselbe in die Musculatur der 



