REPORT ON CEPHALODISCUS DODECALOPHUS. 29 



as in the adult. Posteriorly the body presents, firstly, two lateral chambers with fibres 

 internal to the basement-layer, and secondly, a median (dorsal), with a process of 

 basement-tissue running to the ventral line, and forming the septum between the two 

 former. The pedicle seems to be filled with muscle-cells. 



In the terminal region of the pedicle of the adult certain areas containing a coagulable 

 fluid with globules and granules are present, and occasionally in the elevation caused by 

 a developing bud one or two of them are observed ; and they are also seen in the buds 

 here and there in the course of the central muscles of the pedicle. Some appear to be 

 nucleated. The origin of these bodies is unknown, but they may be connected with the 

 mesoblastic or hypoblastic elements for the buds, though this is only a conjecture. In 

 regard to the presence of the three primary embryonic elements, as a rule, in such buds, 

 the remarks of Professor Haddon ' seem to me to be very interesting, but they have yet 

 to be proved. The doubt remaining in the present case, for instance, relates to the precise 

 nature of the hypoblastic elements. In connection with this subject it is well to state 

 that some observers, as Mr. Harmer, demur to the connection of the latter layer with the 

 origin of the buds. 



As development proceeds, the anterior or disk-bearing region of the body increases 

 much more in proportion than the posterior or pedicellate part. The buccal disk is 

 rapidly enlarged, and shows traces of the broad arch of pigment anteriorly and the 

 reddish band posteriorly, as well as the two median elevations on the surface. The 

 posterior moiety of the disk is especially large. Moreover, the body begins to project 

 outward superiorly, and the papillge of the plumes increase in number. These papUlse 

 form a slightly curved row in front of the dorsal projection of the body (woodcut, 

 fig. 2). 



In the next stage the disk is almost completely formed, though of smaller size and 

 more massive than in the adult. It is thickest anteriorly, much thinner posteriorly. 

 In the former region it presents in transverse section the elongated central chamber, 

 bounded ventrally by the massive hypoderm of the shield, which has the two median 

 prominences observed in the adult. This hypoderm folds over at each side, and is 

 continued as a thinner stratum dorsally, with a basement-layer next the chamber. Two 

 additional structures have now appeared, viz. , a dense (narrow) layer outside the basement- 

 tissue just alluded to, and fan-like fibres from the middle of the dorsal wall of the 

 chamber. Two of the most ventral plumes (the first to appear) have now attained some 

 size, the tip being furnished with the radiate terminal glands having the central chamber, 

 and the sides with short papillse representing the filaments. Both the latter and the 

 axes of the plumes are composed of hypodermic tissue, and are apparently solid. Longi- 

 tudinal striae are visible along the centre of the axis, and they run into the lining of the 

 cavity in the terminal enlargement. Then the central chamber appears dorsally 



1 Quart. Journ. Micr. ScL, N.S., vol. xxiii. p. 34, 1883. 



