BULLETIN OF THE UNITED STATES FISH COMMISSION. 195 



sack is absorbed, just as I have observed in embryo pipe-fishes. There 

 is also in the latter a more decided downward bending of the head as 

 it becomes free from the yelk ; we may expect to see a similar state of 

 affairs in the development of the sea-horse. Beyond this stage in 

 Si/ng7iatJnis an unwonted acceleration in the development in the length 

 of the quadrate cartilage, trabecular cornu (rostral cartilage), pushes 

 the rudiments of the inferior and superior maxillaries forwards so as to 

 lengthen the snout at an unusually early period. In jirofile, the head of 

 the young Lophobranch now bears a suggestive likeness to that of a 

 pug dog. 



From what we know of the early development of the medulla spinalis 

 of Si/ngnathus, according to Calberla,* it is at first solid, as I have found 

 in tne case ot very young embryos of the shad from a study of trans- 

 verse sections. This is also probably the primitive condition in Hippo- 

 campus. 



LATER DEVELOPMENT. 



The specimen of young sea-horse upon which this notice is based had 

 already left the brood-pouch of the male and had been swimming about 

 for a couple of days; its development had accordingly advanced consid- 

 erably. We will begin our description with an account of the embry- 

 onic skeleton, referring to the plate in explanation of the relations of 

 the parts. 



Cartilaginous sJceleton. — The axial rod around which the bodies of the 

 vertebroe are developed, and known as the notochord ch, still persists 

 and extends from behind the pituitary body py to near the end of the 

 tail. At its anterior extremity it is much bent downwards just under 

 the medulla oblongata mo. Farther back there is a slight bend in it 

 where the basalia, or basal cartilages of the dorsal fin el/] almost come 

 into contact with it. In the caudal region it is coiled in conformity with 

 the comijlete turn which is made by the terminal part of the tail. A 

 sheath appears to be developed around the notochord, and rudiments of 

 the vertebral elements have been developed, but they are not yet seg- 

 mented and distinct. 



T7te skull. — There are no true bones yet developed in the skull, all of 

 the cranial bones are still represented by cartilage. The anterior end 

 of the notochord ck is involved in cartilage which arose primitively as 

 the parachordal cartilaginous masses j) on either side and a little past 

 the end of the axial element. Beyond this the trabecuLne cranii t extend 

 forwards under the brain, the si^ace between them at this stage being 

 slight where the piliutary body py lies above it. The cartilaginous 

 basis cranii is extended forwards far bej^ond the eyes as the trabecular 

 cornu, the olfactory organs or nasal pits na lying in an excavation on 

 either side, with an ethmoidal cartilaginous septum, e, between them 

 The tegmen cranii to is developed ujiwards and backwards so as to 

 roof over the fore brain ce. In front of the olfactory j)its na the trabe- 



* Morph. Jahrbuch III, 1877. 



