THE GENUS PTERYGOTUS 193 
Schizopoda and Stomapoda, such as Jfysis, Phyllosoma, and Evichthys, 
either the abdominal or some of the posterior thoracic members, 
or both, became abortive, and that in the larval condition of 
some Podophthalmia, even the sixth pair of abdominal appendages 
remains undeveloped, and the abdomen is wholly devoid of limbs. 
In the larval Brachyura or Zoe@ all the appendages but the gnathites 
and antenne are rudimentary, and the long palpiform maxillipedes 
are (in addition to the abdomen) the only organs of propulsion. 
The larval lobster (before hatching) is similarly deprived of ab- 
dominal appendages, it possesses a disproportionately large labrum, 
and a metastoma, which is only slightly emarginate anteriorly, and 
very large in proportion to the other buccal organs, as compared with 
its adult state. 
In the paper referred to, I laid considerable stress upon the 
analogies, which, from what has been said, may be readily enough 
apprehended, between Péerygotus and the Déastylide@ and larval 
Podophthalmia. Renewed examination of the specimens and of 
the far more extensive materials which have since presented them- 
selves, aided by a careful investigation of the characters of the recent 
Copepoda, has shown me, however, that at least as strong a case might 
be made out for the relegation of the Prferygotz to the latter order. 
(See p. 202, note.) 
The evidence which has led me to this conclusion can only be 
appreciated when the structure of the Copepoda is fully understood. 
1 will, therefore, proceed to give a brief account of that structure, 
and I am the more willingly led to do this as I have found it 
difficult, notwithstanding the valuable labours of Milne Edwards, 
Baird, Dana, and others, to arrive at a clear and connected view of 
the anatomical characters of this difficult group. 
The genus Calanus, containing a large number of marine species, 
is perhaps best fitted to furnish a typical illustration of copepod 
anatomy. The species represented in Plate XVI. [Plate 27] fig. 1, 
was taken in the North Atlantic. It is about one-eighth of an inch 
long, and (after preservation in spirit) has a lightish brown colour. 
The body presents a large carapace anteriorly, succeeded by a number 
of thoracic and abdominal segments. The cephalo-thorax has the 
form of along oval, truncated and slightly excavated behind, the 
postero-lateral angles of its last segment being but very slightly pro- 
duced. The abdomen has not a third the length of the head and 
thorax, and is terminated by two elongated lobes provided at their 
extremities with long seta. The antennules are as long as the body. 
The cephalo-thorax consists of six segments, the anterior of which is 
VvOu, IL 0 
