TEOCHOPHOEE OF HYDEOIDES UNCINATUS (eITPOMATUS). 589 



EXPLANATION OF PLATES 21-23. 



Illustrating Mr. Cresswell Shearer's paper "On the Develop- 

 ment and Structure of the Trochophore of Hydroides 

 uncinatus (Eupomatus)." 



Lettering. 



ces. CEsopliagiis. an. Anus. an. v. Anal vesicle. ajj. s. Apical 

 mnscle-strand. bl. Blastopore. ca\ m. Coelomesoblast. co. Otocyst. 

 e. Eye spot. ect. Ectoderm, end. Endoderm. g. Gut. hlc. Head-kidney. 

 m. Mouth, mesc. Mesenchyme or ectomesohlast. oc. Otocyst. seg. c. 

 Segmentation cavity or blastoccel. Stm. Stomach. 



PLATE 21. 



Fig. 1. — Fully-grown free-swimming trochophore of Eupomatus 

 thi-ee days old. The mesoderm Ininds are just commencing to appear. 

 The head-kidney is shown opening into the proctodieum while the closed 

 end is attached to the oesophagus. This and the subsequent figs. 3, 7 and 

 8 are drawn from living larvaj compressed slightly under a cover- 

 glass. 



Fig. 2. — Trochophore of Hydroides nor vegic a. 



Fig. 3. — Trochophore of Eupomatus four days old, showing the 

 otocyst and mesoderm bands well formed. 



Fig. 4. — Head-kidney in a three-day old larva of Eupomatus. 



Fig. 5. — Head-kidney in larva of Hydroides norvegica. 



Fig. 6. — Trochophoi-e of an iinknown Annelid (probably Hydroides 

 pectinata) from an outline drawing \)j Professor E. B. Wilson, 

 showing the opening of the head-kidney into the proctodseum. 



Fig. 7. — Trochophore of Eupomatus three days old. Seen from the 

 ventral surface, showing the junction of the head-kidney on one side 

 with the gut. 



Fig. 8. — Trochophore of Eupomatus three days old seen from the 

 oral side. The head-kidneys are shown on either side running down to 

 open into the proctodeum. 



PLATE 22. 



Fig. 9. — Whole preparation of a larva of Eupomatus twenty-four 

 hours old. In this and in the subsequent figures of this plate the cilia 



