198 ABTHUB E. SHIPLEY. 



ules, which stain deeply with hsematoxylin, giving the cell a 

 very characteristic appearance. I have been unable to form 

 any opinion as to the nature or fate of these granules. 



The ciliated ring mentioned above is shown in section 

 in fig. 41, c. g. It lies close in front of the most anterior gill- 

 bar ; ventrally its two halves converge and run back as two 

 parallel grooves to the opening of the thyroid gland in the 

 ventral median line. The grooves here unite, and after receiv- 

 ing the opening of the thyroid they continue as a single groove 

 running in the ventral median line as far as the most posterior 

 gill arch. Dorsally the grooves unite and become continuous 

 with a median dorsal ridge, which is covered by high columnar 

 cells, also ciliated. This ridge extends from the first gill arch 

 to the commencement of the cBSophagus. Anton Schneider 

 describes a band of cilia running from this dorsal ridge on 

 each side along each gill arch. This is not present in my 

 oldest larva, but is no doubt formed later. 



Dohrn (23) has recently described the development of the 

 thyroid so fully, and his paper is so beautifully illustrated, 

 that it appears to me to be superfluous to describe again the 

 origin of this organ. I can only confirm his results. He 

 deals at length with the homology of the thyroid of Ammo- 

 coetes, with the endostyle of Ascidians, and the hypobranchial 

 ridge in Amphioxus. And the homology of the circumoral 

 ciliated ring in Ammocoetes and Ascidians is also pointed 

 out. To these homologies we may add, I think, that of the 

 dorsal ciliated ridge of the young larval Lamprey to the dorsal 

 lamella of Ascidians, and the hyperpharyngeal groove of 

 Amphioxus. It is a curious fact, however, that in the last 

 animal the form of the structure is reversed. We find ven- 

 trally a ridge and dorsally a groove, whereas in Ammocoetes 

 and Ascidians we have the ridge dorsal and the groove ventral. 

 In spite of this, I think Dohrn's arguments fully support the 

 homology of the ventral organs, and the same reasoning holds 

 good for the dorsal. 



The alimentary canal behind the branchial region may be 

 divided into three sections. Langerhans has termed these 



