38 T. H. MORGAN. 



pair of pouches projects into that portion of the posterior part 

 of the embryo from which the next pair of appendages arises. In 

 the anterior dorsal part of the larva are seen the first traces of a 

 pair of eyes ; the first pair of appendages is bent towards the 

 ventral surface. 



This embryo was stained and cut, and from the series of sec- 

 tions the following facts obtained : There is a small brain 

 connected by means of a pair of commissures with the anterior 

 ventral ganglion. This first ventral ganglion is, as we saw in 

 the earlier larva (Part I), really a pair of fused ganglia. Behind 

 this lies the second ganglion (the third of the series). The 

 oesophagus, running back from the mouth through the proboscis, 

 opens into the mid-gut. The latter has a pair of prolongations 

 into the base of the first pair of appendages, and another pair of 

 pouches run to the base of the third pair of appendages. The 

 posterior part of the larva contains a backward continuation of 

 the digestive tract, which seems still to end blindly behind. The 

 cells lining the wall of the gut are now quite different from those 

 observed in stage 1, which were seen in Fig. 13, Plate 1. In 

 the present stage (2) they are much larger, are filled with large 

 round masses of yolk-like substance, so that the lumen of the gut 

 is almost obliterated. The yolk-like substance must have come 

 from the exterior, and indicates that the animal is feeding at this 

 stage and, perhaps, is supplied with abundance of food-material. 

 No solid extraneous matter was ever seen in the tract of either 

 larvae or adults of Sea-Spiders, so that the food is probably 

 obtained by sucking the juices of other animals — another simi- 

 larity to Arachnids ! — and probably from the hydroids, amongst 

 which they live. The series of sections did not show any traces 

 of a heart. A single pair of eyes was seen over the brain, and 

 to the sides of these a thickened mass of ectodermal cells. 



Passing to what seems to be the next stage of development, we 

 have an embryo, shown by Fig. XII, Plate V, stage 3. There 

 is quite an increase in size, especially marked in the length of the 

 embryo. The first pair of appendages and the proboscis are 

 longer and larger than in the last. The second and third 

 pairs are as in the preceding stage ; but the embryo now shows 

 clearly external indications of a fourth pair of appendages. 

 The preserved larva was quite opaque, and nothing of the 



