I02 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



Fig. 5 reveals such a condition, in which the muscle plate 

 my^. is at a higher level in the stalk than mf-., and is gradu- 

 ally disappearing, while mf-. is coming in to take its place. 

 For short distances, at intervals, then, the stalk is double- 

 layered. The muscle plates are imbedded in a homogene- 

 ous matrix which possesses no cellular structure whatever. 



The Head. — If the whole of the expanded portion consti- 

 tutes the head, or capitulum, then it must be said to consist of 

 two apparently distinct elements — muscle plates and zooecia. 



The lower portion of the head is the budding region for 

 the muscle plates (fig. i, m. b.) and in their earliest stage a 

 muscle plate cannot be distinguished from a zooecium and 

 its contained polypide. Fig. 3 represents this transitional 

 region, where both polypides {p. b.) and plates {m. f.) are 

 forming. The young muscle plates are characterized by a 

 scattering of the pink-staining cells throughout the contain- 

 ing ectocyst; whereas in an ordinary zooecium the cells des- 

 tined to become a polypide are aggregated near the center, 

 and soon bud out the tentacles and other organs. The 

 ectocyst, too, early acquires the zooecial aperture through 

 which the tentacles are protruded (fig. 3, «.). 



The head is oval in form, and consists for the most part 

 of zooecia imbedded in a gelatinous matrix, similar to that 

 of the stalk, but much thinner. The upper portion of a 

 zooecium is visible on the surface. In the retracted state, 

 the orifice and a portion of the tentacle sheath only can be 

 seen. The remainder of each zooecium containing the 

 major portion of the polypide extends inward toward the 

 central cavity of the head. The zooecia are thus crowded 

 together and overlap to a certain extent, to a greater degree, 

 but in much the same way as the muscle plates of the stalk. 



Polypides in every state of development are found all 

 over the upper portion of the capitulum. Fewkes observes 

 that the more developed polypides lie at the distal pole of 

 the capitulum. This is not confirmed in the present instance, 

 for young polypide buds are found pushing their way 

 between adult zooecia at the distal pole quite as commonly 

 as below that region, while the lower pole is entirely 



