THE LOBSTEE. 
351 
merets, as well as by tbe softness and flexibility of tbe first pair 
of abdominal appendages. The essential generative part (ovary 
or testis) in both sexes consists of a pair of elongated sacculated 
tubular glands with a transverse communication. They lie 
antero-posteriorly beneath the heart. An excretory duct de- 
scends from each gland, and is called in the female the oviduct^ 
in the male the vas deferens. The duct in the female opens 
externally upon the base of the antepenultimate (last but two) 
thoracic appendage on each side. In the male it opens on the 
base of the last thoracic limb on each side. 
The sexual product of the male (spermatozoa) has each 
three tail-like processes, but is nevertheless not locomotive. 
It becomes aggregated in packets (spermatophores) by a viscid 
secretion. A similar secretion attaches the female product 
(ova) to lateral appendages of the mother. In development, 
only a small part of the yelk divides, and gives rise to the 
membraae whence the embryo arises (blastoderm). 
It is the ventral side of the body, i.e. that side of the body at 
which the nervous system is situated, which appears on the sur- 
face of the ovum. The various appendages successively appear 
as buds of similar form and size, and the thoracic limbs for a time 
have both exopodite and endopodite. No apertures ever appear 
in any*way answering to the visceral clefts of the human embryo. 
Such are the main facts concerning the form and structure of 
this highly interesting though common animal. It is interest- 
ing because it presents us with the most fully developed and 
complex condition of that type of structure to which it belongs. 
All crabs, shrimps, insects, scorpions, spiders, hundred-legs, 
&c., belong to the same type, but with more or less important 
modifications. The shrimps are almost the same in structure, 
but the crabs have the abdomen quite rudimentary, devoid of 
appendages, and tucked up on the under surface cf the enormous 
cephalo-thorax. 
In all insects, scorpions, spiders, and hundred-legs the anten- 
nules of the lobster are not represented. 
In insects, the appendages which answer to the second pair of 
maxilla? of the lobster are united in the middle line, and take 
the name of labium. The three pairs of legs with which each 
insect is furnished answer to the maxillipedes of the lobster. 
In the scorpions, the antennse are chelate (as they are indeed 
in the king crab), and the palps of the mandibles, instead of 
being very small structures as in the lobster, are expanded into 
the large formidable-looking claws. Its four pairs of legs 
answer to the two pairs of maxillse, the great claws and the first 
pair of legs of the lobster. The same may be said of the legs 
of the spider. The sting at the end of the scorpion’s so-called 
tail, but real abdomen, is a modified telson. 
