No. 3.] ZHE EMBRYOLOGY OF THE EARTHWORM. 443 
larval types (Polygordius, Eupomatus, etc.), the entire mesoblast 
arises from a single pair of cells (teloblasts), which appear near 
the time of gastrulation in the region of the posterior lip of the 
blastopore, though they may be differentiated before the gas- 
trula stage is reached, as in the foetal types generally. In a 
number of the larval types, however (Lopadorhynchus, Alciope, 
Asterope, Nauphanta, t. Kleinenberg; Pileolaria, Aricia, t. Sa- 
lensky), it is asserted that there are no teloblasts, and that the 
mesoblast is split off from the ventral ectoblast, long after the 
gastrulation is completed. According to Kleinenberg, the meso- 
blastic and neural elements are separated from the ectoblast in 
a common basis (ventral plate) which is afterwards differentiated 
to form a neural plate and a muscle-plate. 
It is much to be regretted that neither Kleinenberg nor 
Salensky has made a minute study of the posterior portion of 
the germ-bands in surface-view. All of Kleinenberg’s illustra- 
tions of the histological detail are made from sections, and a 
careful study of them has not only left me unconvinced in regard 
to the absence of teloblasts, but has given some ground for the 
suspicion that he may have overlooked them —a suggestion 
which I should not venture to make were it not for his previous 
failure to see the eight anterior teloblasts in Lasmbéricus. Thus 
he figures large cells with huge nuclei at the posterior ends of 
the neural foundations in Asterope (No. 31, Taf. 14, Fig. 69) 
and Alciope (l.c., Fig. 67"), which look extremely like sections of 
the neuroblasts in Lumobricus ; and he figures in Fig. 68%, in 
Asterope, a group of large cells at the hinder ends of the meso- 
blastic bands, which, to say the least, deserve further study, for 
it is possible that the mesoblastic condensation has not gone as 
far as in Lumobricus, and that the two primary mesoblasts of this 
form are represented in Asverope, etc., by a larger group. 
The apparently ectoblastic origin of the mesoblast in forms 
under consideration, is by no means irreconcilable with the facts 
observed in the foetal types, though further researches are re- 
quired to show their precise relations. The explanation must, 
I believe, be sought in the relations of the posterior ends of the 
germ-bands to the blastopore, a more precise study of which in 
the Polychzeta is now of the greatest importance. All the evi- 
dence goes to show that the primary mesoblasts arise on either 
side the median line, near the posterior (ventral) lip of the 
