BUDDING PROCESSES OF CEPHALODISGUS DODEGALOPHUS. 525 



grooves, the peri-pharyngeal groove, sub-neural gland, the pharyngeal clefts, 

 and the pleurochords. 



(2) The notochord of the Chordata may be primarily derived from this source as a 



channel for cloacal water from the point of separation to the points of 

 exhalation, i.e., pharyngeal clefts. 



(3) The gonads are suspended in lateral mesenteries, and surrounded by a blood- 



sinus, communicating with the dorsal sinus. 



(4) The pedicle or ventral sucker has a ventral nerve cord and two ventrolateral 



cords, a dorsal and a ventral blood-sinus, and complete inner layer of longi- 

 tudinal muscles. 



(5) The buds arise usually in pairs ventrally. The ectoderm and mesoderm of the 



bud are formed directly from those of the pedicle. The endoderm is formed 

 by invagination of the ectoderm. 



(6) The pharyngeal clefts arise as endodermal diverticula which break through the 



ectoderm to the exterior. From their structure and relationships to the 

 pleurochords in the adult, they would seem to be simply the oral termination 

 of the latter. The two primitive chordate characters of notochord and 

 pharyngeal cleft would thus appear to have arisen from a common rudiment 

 resembling the pleurochord of Cephalodiscus. The anal end of the intestine 

 is at first in contact with the ectoderm posteriorly and just above the 

 pedicle, but later moves up to the oral end and then opens to the exterior. 



(7) The blood system arises as a system of sinuses between the ccelomic cavities 



and the ectoderm, continuous from the first with those of the adult. 



(8) The sub-neural gland arises far out and moves secondarily into connection with 



the sub-neural sinus, u & 



(9) The first three pairs of plumes arise near their final position, into which they 



move gradually with a rotation through 180°, the last three, forming the 

 inner row of the adult, arise in situ. 



(10) The oviducts, proboscis-pores, and collar-pores all arise in a similar maimer, as 



paired ectodermal tubes. 



(11) The gonads arise as proliferations of the mesoderm lining the trunk-ccelome. 



(12) The adult characters are assumed when three to four pairs of plumes are 



present ; and separation from the parent is then effected by constriction. 



(13) The lens of the branchial eyes is formed by cuticular hypertrophy and later ^7 



detachment. 



(14) Sexual development commences in the egg-capsule whilst attached to the inner 



wall of the ccencecium, and results in the formation of a larva segmented 

 into two parts by an annular constriction. 



(15) The pre-oral sac arises as a diverticular invagination of the posterior wall of 



the pre-oral ccelome, and its bounding cells become modified into spindle- 

 shaped excretory cells free in the sub-neural sinus. 



