Prof. Allman on a new genus and species of Entomostraca. 5 



mediately succeeds the maxillae (fig. 19) is well-developed and 

 didactyle, the next (fig. 20) is rudimentary. 



The proper feet (fig. 21) carry two slightly developed rami, the 

 external of which bears some short stiff spines, and the internal 

 is furnished with two or three remarkably long setse not plumose, 

 with a few short ones at their base. 



The internal ovaries may be traced throughout the whole of the 

 thoracic and a considerable portion of the abdominal region, and 

 may already be seen forming a kind of hernia into each of the 

 external receptacles (fig. 15). 



While engaged in the examination of the first of the forms just 

 described as immature conditions of Notodelphys ascidicola, I 

 happened to witness the escape from the ovigerous receptacle of 

 ova which were expelled through the opening already mentioned 

 as existing in the postero -inferior part of this organ. Through 

 the delicate transparent covering of the expelled ova, the form 

 and motions of the embryo could be seen within, and indeed it 

 required in many cases but a few minutes to elapse between the 

 expulsion of the egg and the rupture of its shell by the struggles 

 of the imprisoned embryo. The little larva (fig. 22) thus set free 

 presented itself under the form of an exceedingly active, natatory, 

 arachnoid animalcule with six biramous feet furnished with a 

 pencil of setse at the extremity of each ramus ; the eye-mass, 

 which was of a bright ruby colour, was well- developed, and had 

 the appearance of being formed by the confluence of four distinct 

 ocelli, and the little creature presented altogether a close resem- 

 blance to the young of Cyclops. 



If I am correct in my opinion as to the nature of the different 

 forms now described, we have, during the progress of develop- 

 ment of N. ascidicola from the first rupture of the egg, four di- 

 stinct phases ; that a greater number exist there can be little 

 doubt, but at least four well-defined forms can with certainty be 

 demonstrated. 



The first (fig. 22) is characterized by an absence of distinct 

 segmental division ; only three pairs of feet have as yet appeared ; 

 these exhibit no appearance of the lamellar character, so striking 

 in the more advanced phases; and the intermediate plate not 

 being yet developed, there would seem to be no mechanical ob- 

 stacle to the feet of opposite sides acting independently of each 

 other. The eyes are well- developed and already confluent, there 

 is no trace of antennae, and we have altogether a form which 

 strongly suggests the acaridan type of the Arachnida. 



Between this first stage of the larva and the next in point 

 of development which I have had an opportunity of witnessing, 

 a most striking progress has taken place. It is however almost 

 certain that there arc intermediate stages which I have not yet 



