ZOOL.-VOL. III.] BANCROFT— COMPOUND ASCIDIANS. 1 53 



the coating. But as such colonies could be adequately- 

 described by saying that they were like such a figure with 

 the exception or addition of the coating, they were not 

 figured. 



3. Light coloration of the lower lips of the cloacal 

 orifices (figs, i, 3, 15). This variation also occurred only 

 in Family I; and it was only in two cases that there was 

 the least doubt whether the colony belonged to the class 

 with black or light colored cloacae. Often the cloacal 

 marking would be the first to develop, and would be very 

 prominent, while the rest of the markings were still indis- 

 tinct, as in fig. 15. There were several colonies in which 

 the cloacae, though distinctly belonging either to the light or 

 dark type, were not very strongly marked, as in fig. 11. 

 But what makes the variation so striking here is the early 

 appearance of the light cloacee, and the fact, already 

 noticed in connection with the light-colored coatings, that 

 often two colonies may have exactly the same color except 

 for the difference in the cloacag. There is, then, so far as 

 these three characters are concerned, a decided, though 

 not perfect, discontinuous variation. If this variation were 

 usually associated with other characters varying in a per- 

 fectly irregular manner, it would perhaps have escaped 

 notice. But an important fact to be noticed in this con- 

 nection is, that while, in any chance lot of Botryllus 

 colonies, it is a rare thing to find two that are exactly alike, 

 this is quite common among members of the same family. 

 Thus, in Family II, in a total of six, there were two pairs 

 of colonies that were exactly alike ; and many similar 

 instances were noted in Family I. Now, what makes the 

 discontinuous variation so striking is the circumstance 

 already mentioned, that frequently two colonies are exactly 

 alike except as regards the variable character. This was 

 noticed many times, and is illustrated by fig. 23. When 

 examining variations of this kind, the justice of the contention 

 is impressed upon the writer that there must be something in 

 the germ plasm corresponding, for instance, to the double 

 dorsal bands, and that during development this something 



