Misrellaiicoiis. 445 



s|)iual cord ami the cerebellum, the latter only forming a clavate 

 inflation of the former, as in Ainphioxus. 



On the fourteenth day the young Lampreys, 1 .V line in length, 

 languid, white and opaque, (piit the egg ; they are incapable of 

 rising from the bottom of the vessel. In the inflated extremity of 

 the hinder part of the body are the large cells formed by the seg- 

 mentation of the lower half of the vitellus ; they are filled with the 

 elements of the yelk, and do not entirely disappear for three or four 

 weeks after exclusion. During this period the young fishes take no 

 nourishment. 



After leaving the egg, the branchial apertures are formed suc- 

 cessively by wrinklings of the skin, which attain the number of 

 seven on each side, and become constantly deeper until they reach 

 the pharyngeal cavity. At the same time another wrinkle of the 

 skin produces the mouth ; and above the anterior extremity of 

 the chorda dorsalis, between the skin and the cerebellum, there 

 appears a spot of black pigment, which constitutes the eye. This is 

 formed in the manner of the eye in the Invertebrata. Behind the 

 eye, and near the brain, a large clear cell becomes filled with cal- 

 careous granules ; this is the auditory vesicle, with the otolithes. 

 The heart dindes distinctly into ventricle and auricle, and the peri- 

 pheric portion of the vascular system is developed. Behind the 

 heart some large yellowish cells form the liver. 



At the bottom of the branchial apertures the branchial filaments 

 spring from the partitions ; they are never furnished with vibratile 

 cilia. The cartilaginous branchial arches commence their develop- 

 ment from the chorda dorsalis, and passing beneath the skin of the 

 partitions soon meet beneath, forming a branchial skeleton exactly 

 like that of the mature Lamprey. Beneath the branchial cavity the 

 branchial artery is produced, and between this and the skin a long 

 oval gland, composed of small granulated cells, is formed. It is 

 situated in a cavity with soft walls, which it fits exactly, and its 

 surface is covered with vibratile cilia. The author regards it as a 

 thymus gland, but it does not exist in the mature fish. 



Round the mouth are formed the upper and lower lips, and two 

 lateral flaps united with the upjier lip. The young animal becomes 

 more and more transparent ; but in several parts of its body, espe- 

 cially over the artery and vein beneath the chorda dorsalis, cells of 

 black pigment are deposited in a stellate form. Here also numerous 

 adipose cells are developed, from which some small papillae arise 

 above the heart and liver ; these are directed towards the abdominal 

 side, and oscillate freely ; they also bear on their surface a longi- 

 tudinal range of cilia. The author doubts whether they are the first 

 rudiments of the kidneys or of the Wolffian body, as he subsequently 

 saw the formation of a tortuous canal further back, but still above 

 the liver, which presented no oscillations, and which perhaps would 

 become the Wolffian body, discovered in other fishes not long since 

 by ^L Reichert. When the membranes of the intestine are deve- 

 loped, and the residue of the vitelline mass is consumed, a vibratile 

 epithelium is seen in the posterior portion of the digestive tube. 



