MUSEUM OF COMPARATIVE ZOOLOGY. 103 



nated "anterior " or "oral"; parts nearer the anal end, "posterior" or 

 "anal." To parts nearer the roof of the colony will be applied the 

 term "superior," or "tectal"; to those nearer the sole, "inferior." 

 Parts situated at either side of the sagittal plane of the individual are 

 " lateral," and either right or left, — the individual facing the margin 

 of the colony. In naming organs, I have preferably used the terms 

 employed by Kraepelin ('87). I adopt the term polypide simply be- 

 cause it is a convenient name for a number of organs closely united 

 anatomically, and arising from a common source embryologically. 



II. Architecture of the Colony. 



The colony of Cristatella, as is well known, consists of a closed sac, 

 which is greatly elongated in old specimens, and has a flattened base or 

 "sole," and a convex roof. The wall of this sac is known as the wall 

 of the colony or cystiderm (Kraepelin). Suspended from the dorsal 

 wall, and hanging in the common cavity of the colony, which may be 

 called the coenocoel, are to be seen numerous polypides in different stages 

 of development. A more careful observation shows that the polypides 

 lying nearest the median plane of the colony are the largest and oldest, 

 those nearest the margin, conversely, smallest and youngest (Plate I. 

 Fig. 1). All young colonies of Cristatella have been derived from one 

 of two sources, eggs or statoblasts. According to Nitsche ('72, p. 469, 

 Fig. 1), there are two polypides of the same age first developed in the 

 cystid, which is a product of a fertilized ovum, and regarding these he 

 fully agrees with Metschnikoff's ('71, p. 508) statement, "Die beiden 

 Zooiden entwickeln sich wie gewohnliche Knospen." 



Nitsche ('75, pp. 351, 352) observed that in Alcyonella the primary 

 polypides are placed with their oral sides turned from each other, and 

 that the younger buds arise in the prolongation of the sagittal plane of 

 the older polypides, and from that part of the cystid lying between the 

 oesophagus of the older buds and the margin of the colony. 



As Braem ('89 b , pp. 676-678) has shown, there is but one primary 

 bud in the statoblast embryo. The younger buds formed in the stato- 

 blast arise on the oral side of the primarj' bud. 



In Cristatella, says Braem ('88, p. 508), the newly hatched stato- 

 blast embryo already exhibits to the right and left of the adult primary 

 polypide two nearly complete daughter individuals of unlike age, which 

 are generally followed by two other sisters in the same relative posi- 

 tions, and a fifth in the median plane, — oral with respect to the 



