EOSACETTS, LINCK (COMATULA EOSACEA 0 E LAMAECK). 
531 
the higher animals ; and I have developed the analogy* still further, in tracing the conti- 
nuity of the cavity of the pseudembryonic appendages in Asteracanthion with the vascular 
system of the young Starfish. The sarcode cylinder preceding and afterwards investing 
the embryo of Antedon must undoubtedly be referred to the same category of structures. 
As the development of the pseudembryo proceeds, a large funnel-shaped ciliated 
pseudostome with an obscure intestine and a minute pseudoproct are formed ; and the 
zooid, which at first resembled a Plagiophrys or Difflugia in simplicity of structure, may 
now be compared to a Vorticella or Bursaria. 
The alimentary system is, however, extremely simple. The digestive tract is rudi- 
mentary, and the function of the large funnel-shaped oesophagus, with its loop-like 
pseudocele, seems to be to produce a rapid and special current of fresh water to the 
general mass of absorbent sarcode rather than to localize the assimilative function. 
The functional activity of the pseudembryo appears to reside essentially in the peri- 
pheral layer. During the earlier stages of its development the central portion consists 
of a dusky granular semifluid substance, increasing gradually in opacity, and exhibiting 
active molecular motion; afterwards the centre is devoted to the building up of the 
viscera of the embryo at the expense of this previously secreted pabulum ; hut during 
the earlier stages of the growth of the embryo, its increasing bulk does not appear to 
interfere in any way with the functions of its nurse. Absorption, as indicated by 
increase in size and weight, is at no period more rapid than when the pseudembryo 
is losing its special organs of locomotion and assimilation, and becoming torpid and 
distorted by the growth of the included organism. 
The hollow cylinder of sarcode forming the independent living body of the pseud- 
embryo, at a certain stage loses its cilia, its special organs of assimilation are obliterated, 
it appears to merge its distinct life in a second harmonized combination of organs which 
has grown up within it, and the whole layer, without the slightest change in structure, 
subsides into the perisom of the Pentacrinus. 
Histologically the ectosarc of the pseudembryo must be regarded as having been the 
integument of the Crinoid throughout, its functions highly modified and exalted for a 
special purpose. The hard structures of the perisom, the two rows of cup-plates and 
the stem, are accordingly developed in the substance of this integument ; and the out- 
line of the Crinoid is thus frequently mapped out in calcareous trellis-work before there 
is the least trace of the differentiation of internal organs. The stem has clearly no con- 
nexion with the viscera whatever, it is a temporary appendage to the radial skeleton. 
Until we have accurate details of the embryogeny of a more extended series from the 
various Echinoderm orders, I believe it would be premature to discuss at length the 
morphology of the pseudembryo of Antedon. At present we are acquainted with many 
species belonging to widely differing genera, scattered apparently irregularly through 
the four orders of the subkingdom, which produce independently organized pseud- 
* “ On the Embryology of Asteracanthion vioTaceus (M. & T.),” Quarterly Journal of the Microscopic Society, 
1861, p. 99. 
4 C 2 
