NATURAL HISTORY MISCELLANY. 155 
Lastly, the genital openings in both sexes are situated on the flrst pair of 
abdominal lamellate Fle the testes and ovaries lying wholly in 
the cephalothorax; the ovaries, when distended with eggs, filling up the 
front of the sins dena racic shield 
The abdomen consists of nine sessio, the long spine-like telson 
forming the ninth, as seen plainly in the embryo. e abdominal cavity 
is small, the abdomen being very thin, and mainly filled with the muscles 
attached to the lamellate feet. 
There are, then, in Limulus, no thoracic feet, comparable with those 
of the Decapods and the Tetradecapods, and the thoracic region (as 
much of it as exists), is merged with the head, in fact never becoming 
pee m from the head proper. Thus we have in Limulus a crusta- 
TAX rum potential, viewed externally, with no M or segments 
to indicate its existence) and a nine-jointed abd 
This disposition of the body-segments is vrac iil by the zoéa, or 
young, of the Decapods. In the freshly hatched zoéa the body is divided 
into two regions; the cephalothorax, with no trace at first of thoracic 
nts, Oo 
deciduous maxillipeds), the thorax not being yet omg and a 
five-to-seven-jointed Aia The size of the cephalothorax, com- 
pared with the abdomen, —— greatly in the different forms at Zoés 
hinder portion of the cephalothorax, thus proving our statement that the 
cephalothorax of Limulus, and consequently the so-called **head" of 
Eurypterus and Piéryites, nidore, a head with a potential thorax, 
the latter never becoming differentiated in subsequent moults. 
In the Trilobites, however, according to the late discovery of Mr. Bill- 
ings, the thoracic segments bearing jointed feet are developed; though, 
as shown by Barrande, the larval trilobite is hatched either without any, or 
but a single, thoracic segment. Limulus, Eurypterus, Pterygotus, 
e ite 
D on the ancestry of the members of the subclass * of Bran- 
chiopoda, he would trace them all to a common Nauplius form, as Haec- 
kel, p Müller, and Dohrn had done. This Nauplius form may have 
exi n the Laurentian Period, as we already find highly organized 
eiia. Phyllopods, and Ostracodes in the lowest Silurian strata. He 
d vs his communication to the American Association he has spoken of the pig 
opoda itis he regarded tl the Peeciloptera z as a suborder, he thought the te 
da, etc., they were aus 
more general, groups than me orders of Vertebrates first limited by Linnæus, whose idea of 
H f uniformity, gum as the term family should be applied 
In the sense in which Latreille used it. 
