3o6 BULLETIN OF THE BUREAU OF FISHERIES. 



only to their inner or proximal ends. The eggs, however, are so completely adherent to 

 one another that if every hair were severed the entire cargo would float o£f in a single 

 mass. It should be noticed that the stalks of the swimmerets are inclined inward 

 toward the median plane of the body, and not away from it as in the thoracic region, 

 and also that three tufts of long setae are borne on the inner margin of each, two on the 

 lower part of the inner blade or endopodite, and one on the adjoining end of the stalk or 

 protopodite (fig. 3 and 4, a, c, d) ; further, that upon these setae a vast number of eggs 

 find anchorage, and that glands are very abundant beneath the skin of these parts. Four 

 smaller tufts {e, f, b, g, fig. 3) also carry eggs, and like the former are non-plumose. 

 Assuming that the cement is derived in part at least from the tegumental glands, and that 

 the eggs are engulfed in it when they reach the abdominal pouch, it is difficult to under- 

 stand how in the lobster the true swimming hairs catch so few eggs and in the prawn 

 Alpheus none at all, unless it be due to gravity or the ability of the animal to direct the 

 course of the egg stream while lying on her back and gradually changing her position. 

 The difficulty of explaining this simple fact is not lessened by assuming that the cement 

 originates in the oviducts. 



ORIGIN OF THE EGG GLUE AND FIXATION OF THE EGGS. 



Upon reaching the sea water in the abdominal pouch the eggs are fertilized by the 

 sperm with which the seminal receptacle is charged, and, as seems probable, all are 

 mixed in a secretion coming from the tegumental glands as well as from the oviducts 

 by the beating movements of the swimmerets; the cement gradually becomes viscous, 

 hardens, and eventually incloses each egg in a thin capsule; the individual eggs of the 

 entire mass are eventually fastened to one another and to certain hairs of the abdominal 

 appendages by the spun sheets and threads of the glue. The latter is an ectodermic 

 product and resembles chitin in its appearance and behavior. A knowledge of its 

 chemical and physical properties when combined with sea water, at the time of its 

 secretion, would probably include the answer to a number of puzzling questions. 



There are three subjects, apart from the more special problems of cytology, con- 

 cerning the pairing of the higher Crustacea about which exact knowledge is particularly 

 needed. These are: (i) The exact role played by the cement-producing organ; (2) the 

 kind of stimulus or stimuli needed to arouse the sleeping sperm in its receptacle, set 

 it in motion, and direct its course to the eggs; and (3) more light on the action of the 

 rays, and the "explosive capsule," by means of which recent students have endeavored 

 to explain the forced entrance of the head of the sperm into the egg. Direct obser^'a- 

 tions are too limited at present to afford a basis for the final settlement of any of these 

 matters. 



The origin of the cement has been attributed, on the one hand, to the sexual 

 organs and especially to the epithelial lining of the oviducts, and on the other to the 

 tegumental glands of the swimmerets and lower side of the abdomen and to the 

 egg itself. 



