320 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



mits of the test papilla the ectoderm instead of simply cov- 

 ering the papilla forms convolutions and deep pockets (j>t, 

 fig. n) which greatly increase the surface of contact and 

 secretion. The muscle fibres seem to be attached to the 

 ectoderm by means of the connective tissue lining this layer, 

 and can be seen extending down into the ectodermal 

 pockets. The whole contrivance renders the attachment 

 of the muscles so firm that I have not seen a single case 

 where they have been pulled away from the test. 



It is probable that another result of these involutions is 

 an occasional cutting off of the end of a pocket by a more 

 rapid secretion near the mouth. The cells which were 

 contained in the deeper portion would then become 

 imbedded in the test matrix and give rise to the occasional 

 ectoderm cells there that have already been described. 



The Musculature. 



The fact that the distribution of the muscles in our 

 species and C. macleayanum differs in one important 

 respect has been clearly pointed out by Drasche. He 

 divided the muscles of C. -productum into four classes: (1) 

 The peripheral muscles, situated around the edge of the disk 

 and extending well towards the center (fig. 11). (2 and 3) 

 The circular and longitudinal muscles of the siphons. (4) 

 The twelve series of more or less fan-shaped muscles radi- 

 ating from the siphons and attached to the outer ends of 

 the siphonal ridges. In C. macleayanum, on the other 

 hand, the peripheral system is much less developed and 

 another system is added which is entirely lacking in all the 

 individuals of the western species that I have examined. 

 This is a system of short muscles joining adjacent plates in 

 the extra-siphonal part of the disk. It appears to be the 

 most fundamental type, for all the other classes are refer- 

 able to it without difficulty. They all connect the plates 

 with the test on the other side of a hinge-like thinner area, 

 except some of the peripheral muscles of C. productum, 



