MR. LUBBOCK ON SOME FRESHWATER ENTOMOSTRACA. 207 
the small one at the apex, which, on the contrary, becomes larger and larger, until in 
the seventh pair it is as long as its companion. It also developes on its inner edge a row 
of simple conical teeth. 
The eleventh pair is in the females developed into an egg-cup, as is the case in Apus. 
Apus cancriformis is described as having sixty pairs of legs, of which the first eleven 
correspond to eleven somites, the rest to seventeen or eighteen somites, leaving five or 
six segments to which no legs are attached. This makes thirty-four postcephalic seg- 
ments. According to Baird, however, there are only thirty. In one of my largest 
specimens I found the number of segments to be twenty-eight, exclusive of the head. 
The pairs of legs were forty-two in number. 
Male. After the first notice of the genus Apus by Jacob Frisch in the year 1732, 
more than a century elapsed before the male was discovered. Satisfied that all his 
specimens were females, and laying it down as an axiom that ** aus einem unbefruchteten 
Eye eben so wenig ein lebendiges Thier werde, als aus gar keinem Eye," Schüffer assumed 
that the Apodidz were hermaphrodites, although he was unable to discover any male 
generative organs. Berthold came to the same conclusion, but, in addition, considered 
that he had solved the mystery, and that the semen was secreted in certain sacs some- 
times found among the legs. This supposition was refuted by Zaddach, who, however, 
thought that he had found the male orifice in two small eminences on the posteriór seg- 
ment not far from the median line of the back, and surrounded by three or four spines ; 
these, though with some doubt, he considered to be the retracted penes. 
At the meeting of the German Naturalists at Breslau in September 1833, Professor 
Retzius announced that M. Kollar, of Vienna, had at length discovered the male of Apus. 
Neither Baird, however, nor Zaddach has been able to find any further account of this 
interesting discovery; nor do I find any memoir on Apus attributed to Kollar in the 
useful * Biblographia Zoologiæ, published by the Ray Society in 1852. 
Under these circumstances the credit of being the first to describe the male of Apus 
appears to belong to Dr. A. Kozubowski, Professor in the University of Cracow, who 
has published a memoir on the subject in Wiegmann’s ‘Arch. fiir Naturgeschichte’ 
for 1857. 
The males of Lepidurus productus may be distinguished from the females in the same 
manner as those of Apus cancriformis. In general form there is no apparent difference ; 
but the eleventh pair of legs, which in the female is specialized into an egg-holder, remains 
in the male of the usual type, and is in size and form, as in position, intermediate between 
the ninth and the eleventh pairs. à 
. Among 160 specimens Kozubowski found only sixteen males. Among mine they 
were much more numerous. I examined seventy-two specimens, of which thirty-three 
were males and thirty-nine females. This proportion, however, is probably but little 
to be depended on, since in my case most of the large individuals were males and almost 
all of the small ones were females. Though the greater number of my specimens were 
small, still as it is natural to take the large individuals first, the small ones were doubtless 
more numerous proportionally than my collection would indicate. 
Kozubowski mentions that in Apus the male, though livelier and Songer than the 
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