260 THE STRUCTURE AND AFFINITIES OF HERDMANIA CLAVIFORMIS. 



EXPLANATION OF PLATES XVIII-XIX. 



ABBREVIATIONS. 



cl. 



cl. e'er. s. 



cl. tst. 



cr. 



dt. h'phy. 



dt. rph.' 



ec' drm. 



e'er. dx. 



e'er. s. 



em. 



en'stl. 



ga- 

 ga, rt. 

 gl. n-h'phy. 

 gn. 

 in. 



Ing. d. 

 mb. 



mu. rph. 

 oa. 

 o'dt. 

 oes. 



Mesenchymatous free cells. 



Secreting cells in left epicardiac tube. 



Test-cells. 



Heart. 



Hypophyseal duct. 



Process on rapheal duct. 



Ectoderm. 



Right epicardiac tube. 



Left epicardiac tube. 



Embryo. 



Endostyle. 



Stomach. 



Rectal side of stomach without folds. 



Neuro-hypophyseal gland. 



Ganglion. 



Intestine. 



Dorsal languets. 



Mesenchymatous membrane lining 



subepicardial space and enveloping 



columns of free cells. 

 Rapheal muscles. 

 Ovary. 

 Oviduct. 

 (Esophagus. 



PLATE XVIII. 



Fig. 1. A few zooids from a large colony showing the general relations of the full-grown zooids to the stolons; of 

 the younger zooids to the older ones ; and the form of the zooids. 



Fig. 2. A single zooid removed from the test diagrammatically drawn. The internal organs of the portion of the 

 abdomen between the stomach and thorax may be studied without great difficulty on the entire animal; 

 from about the stomach back, however, the large quantity of reserve material in the mesenchyme cells 

 renders the body opaque, so that this part of the figure has to be reconstructed from dissections and micro- 

 tome sections. 



Fig. 3. A typical branchial sac with the test removed. 



Fig. 4. Typical front view of the branchial orifice in a preserved specimen. 



Fig. 5. The peripharyngeal field, with tentacles and neuro-hypophyseal structures, seen from within. The rup- 

 ture of the tentacular circle and the peripharyngeal band is unfortunate, but otherwise the specimen 

 was particularly favorable for drawing. 



Fig. 6. A fragment of the dorsal part of the branehial sac, showing dorsal languets and transverse membranes. 



Fig. 7. Transverse section of the stomach to show the typical arrangement of the folds. 



Fig. 8. Transverse section of an abdomen in about the middle region. The embryo here cut is in the early blas- 

 tula stage. The mass of cells on the upper side of the embryo is a small portion of the test-cells of the 

 next embryo. 



Figs. 9, 10. Two sections of the same series from the region of the pericardium and heart. They are in order from 

 behind forward. A third section in this same series is shown in Figure 11 (PI. XIX), 



