60 CAUDAL GILLS oi^' ZTGOPTKRID LARV.^, 



itself, and remains unstained by eusin. Aibo, it is bordered, in 

 the hvpodermis itself, by a fine basement-membrane, seen as a 

 dark line under bigh magniiications. Further, in all larval 

 stages except just before ecdysis, a definite pigment-layer inter- 

 venes between the cuticle and the base of the internal lamina, 

 as shown in Text-fig. 3. 



As to the formation of these internal laminae, I must express 

 my agreement with Kis' opinion that this lies partly upon the 

 mechanical side, viz., that they act as additional supports for 

 the alveolar meshwork in the interior of the gill. But they do 

 not exist for this purpose only. They carry the basement-mem- 

 brane of the hypodermis along their entire length; and they 

 show, at frequent intervals, connections with the alveolar walls 

 themselves. It seems almost certain, though it cannot be proved 

 by actual examination, owing to the excessive fineness of the 

 meshwork, that a thin layer of hypoderm-cytoplasm must con- 

 nect all the nuclei of the alveolar meshwork, and that the lamina* 

 are the principal bearers of this cytoplasm into the gill-interioi-. 

 In other words, where single or few hypoderm-cells have passed 

 inwards and helped to form the meshw'ork, their points of con- 

 nection with the hypoderm-layer are indicated simply by the 

 passage of the basement-membrane into the alveolar wall. Hut 

 at those points where masses of hypoderm-cells have been thrown 

 inwards, a lamina is formed, and much of the surrounding mesh- 

 work is probably due to the further ingrowth of the cells carried 

 in along the lamina. Whether the cytoplasmic connections 

 between the scattered nuclei of the meshwork persist throughout 

 larval life or not, we know that they must have existed during 

 the /on) latiou of the meshwork, and that they must continue to 

 exist so far as additions to the membrane are made with the 

 growth of the larva at each ecdysis. I see, therefore, in the 

 internal laminfe, not only a mechanical device for the support of 

 the meshwork, but also the principal carriers of the hypodermis 

 inwards for the formation of that meshwork. 

 The Blood-Cana/s. 



In the abdomen of the larva, the blood travels for?vards 

 through the heart and aorta, backwards in the general body-cavity 



