148 LAEVA OF LIMULUS. 



however, not quite sure whether this first stage really belongs 

 to the larvse, which I am now going to describe, as I did 

 not see it leaving the egg, but consider this to be the case 

 from the form and position of its antennae. In the second 

 stage, which undoubtedly belongs to this series, the body 

 is divided into a thoracico-abdominal portion [the shield 

 being not yet formed] and the jointed spine, the whole 

 Nauplius being of an elongate heart shape (fig. 2 a, 2 b). 

 The inferior part of the body, the future abdomen, is divided 

 into nine segments, separated by a ridge, which gives their 

 edges a spiny appearance. The last of these ends in two large 

 lateral spines. [What seemed to correspond to], the spine of 

 Limulus in this stage consists of seven segments, the last of 

 which ends in a point. Of appendages there are three pairs, 

 the first being just opposite the Nauplius eye, and showing no 

 joints, with three hairs at the top. The second consists of five 

 joints and has a two-jointed flagellum. The third pair finally 

 has about the same number of joints and very nearly the same 

 length, also showing a small flagellum. There are as yet no 

 parts of the mouth, nor does the interior, which is filled with 

 large globules of yolk, show as yet any differentiation. Above 

 the Nauplius eye, which is very conspicuous, we remark a 

 small lens. In this stage the embryo has a length of about 

 0"14 mm., and it is the one in which it was most commonly 

 met with at Zamboanga. 



In the next stage, the third, it has grown a little in size, but 

 shows as yet very few differences from the former stage, except 

 that the walls of the intestine begin to form and show contrac- 

 tions, without as yet communicating with the anal opening 

 (fig. 3). 



After this, one of the most important changes goes on, for 

 with the fourth moulting the shield appears, and the body up 

 to this period, consisting of two divisions only, shows three 

 parts simulating those of a full-grown Limulus, the head and 

 thorax with its shield, the abdomen, and the jointed spine, 

 The Nauplius has now a length of 0-36 mm. (figs, 4 a, 4Z»). 

 The shield is rounded at the edges, just as Milne-Edwards 



