318 
PKOF. K. W. MACBRIDE. 
old which ai*e shown in figs. 17 and 18 the saijie total 
absence of an aboral spike or any indication of its skeleton 
strikes us. The antero-lateral arms are now developed. In 
the larva represented in fig. 17 the skeleton of one post-oral 
arm consists at its base of no less than four parallel rods; 
more distally a curious vestige of latticing is seen in the form 
of short rods accompanying the main rod and each connected 
with it by a transvei’se bar. The ends of the body rods are 
in-bent in a crook-like fashion such as occurs in the normal 
larva of'Echinus esculentus. The larvae represented in 
fig. 18 has an almost normal Echinocardium skeleton in each 
of the post-oral arms, but it is absolutely devoid of the aboral 
spike. In fig. 19 a hybrid six days old is represented; it 
shows much the same features as those shown by the five-day 
hybrid represented in fig. 18, only the arms are better 
developed and the crook-like in-bending of the aboral ends of 
the body rods is very marked. We notice also that a 
recurrent rod is well developed. In the seven-day larva 
shown in fig. 20 one of the antero-lateral arms has been 
absorbed — a phenomenon which often occurs with normal larvae 
which are not quite healthy. The skeleton of this larva 
shows hardly any ti-ace of the maternal influence ; it is almost 
purely of the paternal type. 
None of the hybrids lived longer than eight days although 
they wei-e supplied with abundant food. Three of these eight- 
day larvae are represented in figs. 21, 22 and 23. That 
shown in fig. 21 has a skeleton almost purely paternal in 
character; the only hint of maternal influence is to be seen in 
tlie thorns besetting the single rods which constitute the 
skeleton of the post-oral arms. One striking maternal character 
is, however, shown in the duplicity of the madreporic 
por e . The larva shown in fig. 22 has a double rod in each post- 
oral arm, but on one side the two rods are fused into one for 
the middle of their length, whilst on the other they are widely 
separated from one aiiother and connected by a few cross- 
bars. Finally in the remarkable larva shown in fig. 23 there 
is a skeleton of a purely maternal type, and the aboral spike 
