550 E. W. SEXTON AND ANNIE MATTHEWS. 



eggs, mates with that one first, and then with the others in succession. 

 If, however, he is placed with only one female, and that one with very 

 young eggs, he does not attempt to take her until the eggs are five or 

 six days old, and neither would the female permit herself to be carried 

 by him till tlien. We have a few records of a male carrying a female 

 for this length of time, eight or nine days before the young are 

 extruded from the pouch, but he will only do it when there is no riper 

 female present. I'he relative size of the male and female in mating 

 does not seem of much importance ; at times a big male will take a 

 very small female, and vice versa. 



We have watched the whole process of the moulting of the female, 

 followed by fertilization and oviposition, and find that it is practically 

 the same in our species as in Gammarus index, as described by Delia 

 Valle (1). 



In the case watched, the last young one of the previous brood was 

 extruded at 2 p.m. (December 14th, 1912), while the male was holding 

 the female. Tliey swam about together afterwards, stopping occasion- 

 ally to seize and eat pieces of ulva. 



A periodic convulsive movement on the part of the female, increasing 

 in frequency and violence, led up to the casting of the skin at 7 p.m. 

 the following day. Meanwhile the male employed not only the second 

 gnathopods, but the first and second peraeopods as well in holding the 

 female. At times the male arched himself, bringing the urosome up 

 to rest against the fifth peraeon-segment of the female, and then 

 suddenly straightened out, rasping the uropods along the female's 

 cuticle. During the whole time the male kept the lower antennae bent 

 over the head of the female, so touching both pairs of her antennae. 

 About two hours before the moult the female commenced a series of 

 violent rapid jerks, bringing the head and urosome together, and then 

 straightening suddenly, at intervals stiffening the body in the form of 

 a comma, with the head bent downwards, the body moving with a sort 

 of convulsive tremor. Tinally the male ceased swimming, and they 

 both lay quiet, while the female, helped by the male, freed the head 

 from the old cuticle with the gnathopods. This process and the 

 ensuing rest occupied not more than five minutes. Then the male 

 suddenly arched the body as before, and in straightening again pushed 

 off the posterior portion of the moult with his uropods, assisted by the 

 upward heaving of the female's body. He did not relinquish his hold 

 for a moment. After moulting the female lay absolutely still, without 

 even a movement of the pleopods, while the male kept up a steady 

 current with his. In a few minutes they commenced to swum as 

 before. 



