424 COMPARATIVE ANATOMY CHAP. 



with long 1 eceea which project into extremities 1,4, 5, 6, 7, some- 

 times as far as the terminal joint. 



The anus lies at the end of the hind-body. Special respiratory 

 organs are wanting 1 . The heart has 2-3 pairs of ostia ; its dorsal 

 wall is formed by the dorsal integument. 



The sexes are separate. The sexual glands are paired tubes, which 

 extend through the trunk at the sides of and above the intestine, and 

 are connected behind the heart by an unpaired piece. They give off' 

 accessory tubes into the extremities 4-7, which emerge on the 2d joints. 

 In the male, however, the genital apertures are wanting in the 4th 

 pair of extremities, and generally also in the 5th. In Pycnogonum and 

 Rhynchothorax only one aperture is found on each side in the females, 

 and this is in the 7th pair of extremities. In the males, in the fourth 

 joint of extremities 4-7 cement glands (coxal glands?) are found, 

 whose secretion glues the eggs which issue from the female genital 

 apertures into balls, which are carried about by the male on the 3d pair 

 of extremities, transformed into egg-carriers. 



We find glands which are considered as excretory organs in the 

 2d and 3d pairs of extremities, emerging on the 4th or 5th joints. 



Ontogeny. Most Pycnogonidcc pass through a more or less complicated metamor- 

 phosis. The youngest unsegmented larva carries 3 pairs of extremities, correspond- 

 ing with extremities 1, 2, and 3 of the adult. The first ends in a claw. In spite 

 of the agreement in the number of extremities this larva shows no near agreement 

 with the Naiijilit/s larva, and the extremities themselves, since they all consist of 

 only one row of joints, do not show the character of the Nauplius limb. In the next 

 stage new segments appear at the posterior end of the body and differentiate in the 

 order from before backward. The enteric cceca at first do not project into the 

 extremities. 



The cause of the entrance of enteric cceca and lateral tubes of the sexual glands 

 into the interior of the limbs must be sought in the extraordinary reduction of the 

 trunk and in the great longitudinal development of the limbs. 



The Pantopoda seem to occupy an isolated position among the Arthropoda. On 

 account of the want of a typical Nauplius or Zocva larva we are not justified in 

 placing them near the Crustacea, and they show no evident relation to any other class 

 of Arthropoda. Many zoologists consider the Pantopoda to be related to the spiders, 

 and establish the following homologies for the limbs. Extremity l = chelicene or 

 falces ; extremity 2 + the paired piece of the proboscis lower jaw and pedi- 

 palps ; extremities 3-6 = the 4 pairs of legs of the spider. Extremity 7 is want- 

 ing in the adult spiders, but it is pointed out that in a few Arachnoidca the 

 rudiments of paired extremities temporarily appear on the abdominal segments 

 during embryonic development. On the other hand it must be remarked that the 

 connection of the two paired pieces of the proboscis of the Pantopoda with the 

 second extremity, and the homology of the two parts taken together with the lower 

 jaw and pedipalp of the Arachnoidca, is by no means proved. The inner organisa- 

 tion and the development give little footing for a special comparison of the Pantopoda 

 with the Arachnoidca, since the coaca of the mid-gut have no great morphological 

 significance. 



The Pantopoda are exclusively marine. Niiiiiphvn, Pallene, Phoxichilidium, 

 Ammothea, Pycnogonum. Collosscndcis gigas is a gigantic form in the deep seas. 



