INTERNAL ANATOMY 245 



When these spines elongate, bars are formed between A and D, D and C, C and E, 

 E and B. These intermediate spines limit the spaces in the meshwork and also increase 

 the number of these spaces in almost geometrical ratio. Between diverging pairs of 

 spines lateral bars are formed on this system, but when two spines run parallel to one 

 another, as A and X do, a number of bars may be formed between them without inter- 

 mediate spines. This meshwork is the inhabited part of the colony, beyond which the 

 spines project. 



The spaces between the bars on the surface form the openings for the zooids, but as 

 the spines increase in length and new bars are developed above the older ones, the former 

 openings become part of the internal meshwork. 



In some branches the upper half is slender and pliable ; this represents the growing 

 part of the colony. When first formed the coenoecium is almost transparent and the 

 spines are short and slender, but later by the successive deposition of coenoecial sub- 

 stance, the internal meshwork becomes thicker, and the spines stiff and straight. 

 Between the fully developed colonies and the newly formed semi-transparent pliable 

 pieces, branches representing different stages of growth are found. The differences 

 between them consist mainly in the thickness of the branch, the length and thickness 

 of the spines, and the colour of the coenoecium. 



The zooids are small and measure i -8 to 2 mm. from tip of arms to base of body. There 

 are always five pairs of arms which are 0-9 to i mm. long and possess end-swellings 

 with refractive beads. The stolon which is 1-3 to 1-7 mm. long originates from the base 

 of the trunk and carries two to five buds. The rest of the anatomy agrees with that of 

 C. dodecalophus . 



INTERNAL ANATOMY . 

 ORIENTATION 



Two opinions are held about the orientation of the zooid. Ridewood considers the 

 long axis of the body as longitudinal, while Harmer (1905, p. 23) regards this as trans- 

 verse. The reason advanced for this view is that a section of the adult zooid passing 

 through the collar region and proboscis at right angles to the long axis of the body shows 

 all the five coelomic cavities like a frontal longitudinal section of Balanoglossus. Con- 

 sidering the U-shaped alimentary canal, the positions of the proboscis and the anal 

 opening, this seems very acceptable. But with the lack of adequate knowledge of the 

 development this opinion has at least one difficulty; during the development of the bud, 

 before the arms are formed, the coelomic cavities are arranged in the long axis, so that 

 a section passing medianly through the long axis shows the same arrangement of the 

 coelomic cavities (Fig. 6) as a longitudinal section of Balanoglossus . At a later stage, 

 when the arms are developed, the proboscis shifts forward and the coelomic cavities 

 take up the new positions seen in the adult. Although the condition in the young bud 

 is not regarded as the basis for correct orientation, it has been found convenient to 



