56 CALIFORNIA ACADEMY OF SCIENCES. 



over others, so that in part the two layers are interwoven. 

 It is also an interesting fact that not infrequently fibres 

 may be seen to branch off from a circular bundle and 

 pass into, and become a part of a longitudinal bundle. 



4. THE PHARYNGEAL APPARATUS. 



To find some typical arrangement as to number, form 

 and position of the tentacles, has been an object of much 

 search, and this the more because of the unqualified 

 statements on this point by Herdman ('91) with refer- 

 ence to the other species of the genus, and by Garstang 

 ('91), with reference to P. Lister/'. After examining a 

 very large number of specimens, I believe the question, 

 as I have treated it in the diagnosis, is as nearly definite 

 as the facts will permit. In the fully compound colonies 

 I have found in some individuals fourteen, in one at least 

 eleven, and in another ten. As to length and distribu- 

 tion, fig. 20 illustrates an average condition. There are 

 almost as many different lengths as there are tentacles, 

 the shortest being mere buds, while the longest are of 

 considerable length. The longest are generally situated 

 nearest the peripharyngeal band. 



In fig. 21, pi. ii, the tentacles of an ascidiozooid from 

 one of the crowded but not compounded colonies are rep- 

 resented, and the arrangement above mentioned is here 

 particularlv well seen. A noticeable difference between 

 the two specimens shown in these two figures is seen in 

 the fact that in fig. 21 the shortest tentacles — the ones 

 situated nearest the branchial orifice, are placed upon a 

 low, circular ridge, a sort of velum, extending entirely 

 around the orifice. This I have never seen in the fully 

 compounded forms. In the crowded forms the number 

 of tentacles is greater, also, by about six on an average, 

 though here again I have found as many as twenty in 



