Malformations of Ascophy Hum and Desmarestia. 23 



pseudo - cortex of Desmarestia, as seen in longitudinal section (fig. 5). 

 The walls are generally thinner, however, and the cells much smaller than 

 the normal tissue. The cells are very full of contents, and the dark yellow 

 mucilage, as well as the granular substance, which I found in Rhodymenia 

 palmata, are here in abundance. The Rhodymenia galls, it may be re- 

 membered, were also caused by a copepod, Harpacticus chelifer. In some 

 cases the tissue is torn, and an opening communicates with the outside, 

 looking as if some animal had forced its way through the cells into the 

 open. The space is always half rilled with the fine granular matter 

 mentioned above, and the cells bordering it are very small and thin-walled, 

 showing that some reparative process has been going on around the torn 



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cells. In cutting open some of the larger swellings, a quantity of oblong 

 brown cells pour out, sometimes separate, sometimes adhering together ; 

 and, in nearly every case where these brown cells are, there may be found 

 a specimen of the copepod which causes the outgrowths. I cannot in 

 any way account for the fact that, notwithstanding the large number of 

 outgrowths examined, I have found so few copepoda indeed, in the 

 whole investigation, I have only succeeded in teasing out one fully 

 developed specimen, the others being all rolled up in a more or less 

 immature condition. 



In the case of Rhodymenia palmata, I took the view that the copepod 

 went through its various stages of development in the thallus of the Alga, 

 and on reaching maturity it forced its way out into the open. This view 

 was strongly opposed by an authority on Crustacea, and, until the eggs 

 of the animal are found in the youngest outgrowths, it is impossible 

 that this idea can be more than a theory ; but, if it is incorrect, I cannot 

 understand how the animal comes to be found in the outgrowths before 

 it is fully developed and while still in the nauplius state. 



In Rhodymenia palmata, the small galls in which the tissue was quite 

 undisturbed were probably caused by irritation, which had spread over 

 the adjoining area round the invaded spot of the Alga, and in the case of 

 Desmarestia I account for the presence of the small outgrowths of un- 

 disturbed tissue near the nidus of the copepod in the same way. The 

 isolated swellings, however, on the young branches of the thallus must be 

 formed singly by a puncture or other invasion, as they are too far away 

 in many cases from the scene of disturbance to be accounted for on the 

 score of irritation. Their structure is the same as that of the larger 

 swellings (plate VII., fig. 6), and many of the cells contain darkly coloured 

 matter. 



I have sent specimens of the copepoda, teased out from the mature 

 outgrowths, to Dr. G. S. Brady, who was so kind as to interest himself in 



