88 OTTO F. KAMPMEIER 
agrees with Hoyer that it makes its appearance in approximately 
6-mm. embryos (Rana palustris, R. virescens, R. sylvatica).™4 
He observed that during this period the heart is situated dorsal 
to the posterior end of the pronephros and arises from the 4th 
intersegmental vein, thus differing from Hoyer. Knower does 
not state explicitly how it originates, but I assume that he regards 
it as a local expansion of the vein. According to him, the heart 
opens directly into the plexiform venous sinus of the pronephros 
just back of the last nephrostome. Striated muscle fibers appear 
early in its walls, and in 8-mm. embryos already are arranged in 
bundles which branch freely; he believes that these fibers are 
derived from the adjacent myotomes, the fourth and the fifth, 
since the heart is developed in the intersegment in proximity to 
the ventrolateral portions of these muscle segments. Finally, he 
notes the development of valves at both the afferent and efferent 
portal of the heart. 
A very brief preliminary account of the development of the 
anterior lymph hearts in Bufo was presented by the writer before 
the American Anatomists in 1916. 
Morphogenesis 
Except that they state definitely the time of appearance and 
the location of the anterior lymph heart in frog embryos, neither 
Hoyer nor Knower offers a detailed description of its formation; 
their accounts are brief and rather general. After more extensive 
study, in which numerous graphic reconstructions and some wax 
models were made, the writer is able to demonstrate with greater 
preciseness, perhaps, its origin and progressive changes. Such 
an exposition will show that, in Bufo embryos at least, its genetic 
history and the nature of its changes are not so simple as Hoyer’s 
and Knower’s descriptions would lead us to suppose. ‘The first 
indefinite rudiments are already suggested in approximately 
4-mm. embryos (Bufo vulgaris), thus appreciably earlier than 
14'The early origin of the anterior lymph heart in the frog was indicated by 
Kknower five years earlier (before the American Society of Zoologists, 1903), two 
years before Hoyer’s first paper on the development of the lymphatics in the frog 
appeared. 
