58 Notes from the Gatty Marine Lahoratory. 



Fiy. 22. Transverse section of the refxion in front of iig-. 21, in which the 

 operoulnr .-.talk is separatino- and the slits {hf.) for the forma- 

 tion of the branchial tilanients making- rajiid progress on the 

 other side. On the ventral surface (h'fl in the figure) the 

 tlioiacic coUar is free. Similarly magnilied. 



Fig. 23. rran'«ver>e section after the separation of the opercular stalk 

 and when slits are appearing; on the left or opercular side 

 (upper in tiie figure). The great e.xpanse of the vestibule, d., 

 is noteworthy; «., branchial nerve, the others lie toward the 

 inner ends of the slits. Only the inner branchial nerve, ?«., is 

 indicated in tliis figure. 



Fiy. 21. Transverse section of the tip of a branchial hlament of the fore- 

 sroing. The blood-vessel occupies the centre. It is richly 

 cilinted in life. X oc. 2, obj. D. 



Fiy. 2o. Longitudinal s^^ctiou oi i\ Qhununt of roinatucerus triqueter, L., 

 witli portions of pinnules. X oc. 2, obj. D. 



Plate V. 



Fig. 26. Ti'ans verse section of the anterior region of Pomatocerus tri- 

 queter, L., with the tliorncic glands, tg., in full develo])ment, 

 that on the left showing the origin of the duct which joins 

 that of the opposite side at the median outlet {tgo. in 1*1. III. 

 tig. 15 ioxBispira). cm., cellular appendix of the thoracic gland; 

 d., oesophagus with its chloragogenous coat; dm., dorsal longi- 

 tudinal muscles; hyp., modified hypoderm ; vi.^, special anterior 

 median muscular layer on the dorsum ; m.'^, special ventral 

 layer of muscle ; nc, uerve-cords. Above the gullet is the 

 dorsal blood-vessel in the median mesentery, and a space 

 occurs above it between folds of mesenterj', but soon disappears. 

 X about 35 diam. 



Fiy. 27. Transverse section of the body-wall toward the posterior region. 

 The dorsal muscles, dm., are of great size, with scarcely a 

 trace of separation in the mid-dorsal line ; vm., ventral 

 muscles ; vv., ventral vessel with chloragogenous cells ex- 

 ternally. The outline of the gut is T-shaped. X about 35 

 diam. 



Fig. 28. Transverse section of an anterior foot with tlie hook-jiad about 

 the level of the diminishing thoracic gland, tg. ; ah., incipient 

 muscular fibres of the process oppo.site the external papilla, j). 

 In this section none of the peculiar clavate nucleated cells are 

 visible, x oc. 2, obj. A. 



Fiy. 29. .Section behind tiie foregoing cutting the superficial part of the 

 hook-pad, and showing the greatly developed hypodermic 

 cells with the nuclei situated externally, and forming an elastic 

 cushion in connection with the dense row of minute hooks. 

 ty., thoracic gland. X oc. 2, obj. A. 



Fiy. 30. Transverse section of the opercular stalk in another example, in 

 which the central area is chordoid or areolar in aspect. The 

 nerves are not entered. X oc. 4, obj. A. ^ 



Fiy. 31 , Tr.msverse section of the alimentary canal, showing lateral folds 

 of the mucous membrane, almost valvular in appearance. 

 X 350 diam. 



