198 ARTHROPODA 



Montgomery : Studies on the Habits of Spiders, Particularly Those of 

 the Mating Period. Proc. Acad. Nat. Sci., Philadelphia, 1903. 



: On the Spinnerets, Cribellum, Colulus, Tracheae and Lung-books 



of Araneads. Proc. Acad. Nat. Sci., Philadelphia, 1909. 



The Development of Theridium, an Aranead, up to the Stage of 



Reversion. Jour. Morph., 20, 1909. 



The Significance of the Courtship and Secondary Sexual Charac- 



ters of Araneads. Am. Nat., 44, 1910. 

 Peckham: Observations on Sexual Selection in Spiders of the Family 



Attidae. Occas. Papers Nat. Hist. Soc, Wisconsin, 1 and 2. 

 Wood: Autotomy in Arachnida. Jour. Morph., vol. 42, No. 1, 1926. 



PHOXICmLIDIUM 



The exact affinities of the pycnogonids to other forms is 

 not known, but they have certain characters that have sug- 

 gested a possible relationship to the Arachnida. They are 

 frequently found in considerable abundance on the material 

 that is attached to piles. Notice their movements and see 

 how they cling to the material on which they are moving. 



1. The body is very slender and is composed of a number 

 of free segments that form the head and thorax and a small, 

 vestigial abdomen. How many free segments are there? At 

 the anterior end is a rather prominent proboscis, with the 

 mouth at its end. 



2. The following appendages will be found: 



(a) The chelicerae. What is their structure? Are they 

 armed with pincers? 



(£>) Four pairs of long walking legs. How many seg- 

 ments have they? The viscera extend into the bases of these 

 appendages. 



(c) The male is provided with a pair of ventral appen- 

 dages called the ovigerous legs, by means of which the eggs 

 are collected as they are laid by the female. These appen- 

 dages are not present in the female. 



Make a drawing of the under side of a specimen. 



Cole: Pycnogonidia of the West Coast of North America. Harriman 

 Alaska Exped., 10, 1904. 



