MUSEUM OF COMPARATIVE ZOOLOGY. 75 



rise to new polypides. As a matter of fact, the secondary rows often 

 make a greater or less angle with the primary ones, and as a result 

 lateral branches are formed. Taking this character into account, the 

 Cristatella formula might be written : — 



* b 



* a^ — a I 



I w 



*^ — * a — A 



I 

 (6) • *b - [*]B - [^] 



I 

 *a — a 



This representation indicates the fact that the first formed buds (A, a, a, 

 etc.) are lateral ones ; the second, median (Davenport, '90, p. 106). 

 Intermediate stages between the condition in Plumatella, in which an 

 indefinite number of polypides and gemmiparous masses can be budded 

 off from pre-existing gemmiparous masses, and the condition in Crista- 

 tella, in which only two such ai'ise, occur apparently in some species of 

 Plumatella, in which, as Braem ('90, p. 31) has shown, few polypides 

 are produced from any gemmiparous mass, and all but two of these gen- 

 erally do Jiot develop. In the young corms of Cristatella, on the other 

 hand, more than two polypides may thus arise. 



Other Ctenostomata show a regularity in the budding process similar 

 to that of Paludicella, and exhibit instructive variations upon it. 



Victorella, an interesting Ctenostome occurring in slightly brackish 

 water, and first described by Kent ('70) in 1870, possesses, according to 

 the pregnant observations of Kraepelin ('87, pp. 75, 76, 154-157), a 

 stolon-like tube, from which at intervals polypide-bearing " cylindrical 

 cells" arise. Ki-aepelin ('87, pp. 155-159) has shown it to be in the 

 highest degree probable that the protrusion of the body wall in the neck 

 region of the polypide of Paludicella is the homologue of the " cylindrical 

 cells " of Victorella, and that the remainder of the zooecia of Paludicella 

 is homologous with the " stolon " of Victorella. While in Victorella the 

 cylindrical cell is developed to such an extent that the retracted poly- 

 pide is still included within it, and the stolon remains of small calibre, 

 in Paludicella, owing to its shortening, the retracted polypide must seek 

 refuge in the stolon, whose diameter is consequently inci^eased to receive 

 it. Evidence for this is found in the stolon-like natui-e of the youngest 

 zooecia of a hatching winter bud of Paludicella Ehrenbergii, and in the 

 elongated cylindrical cell of the adult Paludicella Miilleri, Kraepelin, 



