118 Part III. — Twenty-second Aniiual Report 



the adhesive property had completely disappeared." The stickiness is 

 not a true cement, it is merely an albuminous substance, not a fluid 

 ' chitin " capable of forming an outer envelope. 



While it is not easy to say exactly how the stalked attachment between 

 the eggs is produced, it is still possible to describe a process by which 

 the same might be arrived at. 



I have not seen the newly-extruded egg, but assume that on passing 

 out of the oviduct it will show little if any perivitelline space. The 

 egg in gaining contact with sea-water would immediately begin to deve- 

 lop a perivitelline space. The extruded eggs lying on the abdomen 

 would, by the mutual pressure due to their weight, tend to cause the 

 expulsion of some of the perivitelline fluid by the micropyle (which, 

 although it has not yet been described, very probably exists). Through 

 this the now flaccid chorion might be glued to an egg, which in a similar 

 way might attach itself to a third or to the first egg. Again, these eggs 

 may have been pierced by the hairs without actually becoming attached 

 to them. The eggs that are attached to one another are close to the 

 base of the pleopod, where they are not subjected to any very violent 

 movement. They are often found on the outside of the eggs which are 

 attached to a fascicle of hairs. 



The weight of the egg tends to stretch out the ductile chorion into long 

 thin stalks. Two attachments may sometimes be seen to one broad stalk. 



Nephrops norveijicus. — The pleopod is short and paddle-like ; the endo- 

 podite is 2-jointed. Both branches are fringed with densely plumose 

 seta3. The egg-hairs (fig. 64) have sharp points, and are ciliated near 

 their extremities ; the cilia are small, soft, and blunt. Sometimes the 

 fourth of the length of the hair is ciliated. The egg-hairs are arranged 

 round the periphery of the hind surface of the endopodite ; they are 

 also found on the protopodite. At the joint on the endopodite the 

 projecting corner of the proximal segment bears a fascicle of egg-hairs. 

 The egg-hairs do not carry nearly so many eggs as they do in the 

 Brachyura. 



Crangon vtdgaris. — The egg -hairs are short, but more than one egg is 

 strung on one hair. The eggs are attached to the protopodite, not to the 

 endopodite or exopodite. 



Pandahis Montagui. — In this form also the eggs are attached to the 

 inner surface of the protopodite, and not to either the endopodite or exo- 

 podite. The egg-hairs are short. 



The eggs are also attached to one another as in the lobster. 



The duty of bearing the eggs is not allowed to interfere with the swim- 

 ming function of the pleopod. In Crangon and Pandalus, where the 

 pleopods are important swimming organs, the eggs are attached to the 

 protopodite. 



In Homarus, where the swimming function of the pleopod is prac- 

 tically in abeyance, the eggs are attached to the endopodite and exopodite, 

 but not to their distal parts. 



In the Brachyura, in place of a pleopod which performs both functions, 

 viz. of swimming and of carrying the eggs, we have an organ which is 

 suited solely for bearing and protecting the eggs. The endopodite is 

 provided with special hairs to which the eggs become attached, while the 

 exopodites function in protecting the attached eggs during the period of 

 incubation. 



Carcinus mamas. 



The writer had the opportunity of observing part of the spawning 

 process in Carcinus. Four females extruded their eggs at the Laboratory. 



+ P. Mayer 



